Items! There are many items in Undertale. You can find them, use them, and throw them away, if you wish. This list covers all of 'em.

Items in Undertale can only be sold to the Temmie vendor in Temmie Village. The sell prices here are only base sell prices; the Temmie will occasionally offer you a premium on items he really fancies. Reject the first price and accept the second. Try to go any further than that and he'll flat-out refuse you, with some slightly chilling results.

Main Walkthrough

 Weapons

 Stick

Attack: 0
Location: The Ruins
Buy / Sell Price: None; 150 gold

Your starting weapon. All it does is allow you to attack. Yay?

Torn Notebook

Attack: 2
Location: Waterfall
Buy / Sell Price: 55 gold; 50 gold

The alternate weapon in Waterfall. The Torn Notebook is a solid item, despite being weaker than the Ballet Shoes, because it grants you extra seconds of invincibility when you get hit.

Toy Knife

Attack: 3
Location: The Ruins
Buy / Sell Price: None; 100 gold

The second weapon in the game. Weak, but better than the Stick. You'll find it just before reaching Toriel's little house at the end of the Ruins.

 Tough Glove

Attack: 5
Location: Snowdin
Buy / Sell Price: 50 gold; 50 gold

The third weapon. The Tough Glove allows you to strike multiple times by tapping the Z button. The more you tap, the harder you hit. You can purchase the Tough Glove in Snowdin, but there's no point, as you can find it for free in the first Box you encounter.

Ballet Shoes

Attack: 7
Location: Waterfall
Buy / Sell Price: None; 80 gold

Weapon number four. You'll find the Ballet Shoes in a bush, 'round a third of the way through Waterfall. You can attack three times in one round with the Ballet Shoes. (This is misleading, of course, but they do still do more damage than any previous weapons.)

Burnt Pan

Attack: 10
Location: Hotland
Buy / Sell Price: None; 100 gold

Found on a ide area from the first set of hopping panels in Hotland. The Burnt Pan hits four times. Not much different from the Ballet Shoes. The major difference is the fact that the Burnt Pan will, when equipped, add an additional four HP whenever you use a restorative item. It would probably be great for a Pacifist run if you had more than twenty HP, but, you know, you won't. So.

Empty Gun

Attack: 12
Location: Hotland
Buy / Sell Price: 350 gold; 100 gold

Purchasable from Bratty and Catty, outside the MTT Resort. It's an okay weapon, but not enough of a jump in quality over the Burnt Pan for the price.

Worn Dagger

Attack: 15
Location: New Home
Buy / Sell Price: None; 250 gold

The best weapon you'll find in most runs, namely Neutral and Pacifist. The Worn Dagger is located in Asgore's home.

Real Knife

Attack: 99
Location: New Home
Buy / Sell Price: ---

By far the strongest weapon in the game, and needlessly so, since you'll only use it once. The Real Knife is found in Asgore's home during a Genocide run, in the same place you would normally find the Worn Dagger.

Armour

Faded Ribbon

Defence: 3
Location: The Ruins
Buy / Sell Price: None; 100 gold

The second piece of armour you can find. Worth grabbing, if you can find it. Look in the six pits near the end of the Ruins.

Cloudy Glasses

Defence: 5
Location: Waterfall
Buy / Sell Price: 30 gold; 50 gold

Though it's statistically worse than the Old Tutu, which you find in the same area, the Cloudy Glasses are overall the better item for completing Waterfall. This is thanks to their special power, granting you a few extra seconds of invincibility whenever you get hit. This makes them very useful when fighting Undyne. (You can also make a profit off these by buying a whole bunch and walking to the Temmie Village to sell them, though that gets tedious pretty quickly.)

Manly Bandanna

Defence: 7
Location: Snowdin
Buy / Sell Price: 50 gold; 50 gold

More armour. You can buy it in Snowdin. Might as well.

Old Tutu

Defence: 10
Location: Waterfall
Buy / Sell Price: None; 80 gold

Yet more armour! You'll find it behind the first waterfall in Waterfall, in the same section as the falling blocks of ice. 

Stained Apron

Defence: 11
Location: Hotland
Buy / Sell Price: None; 100 gold

An upper tier of armour. The Stained Apron will heal one HP every other turn while it is equipped. This sounds underwhelming, and... well, it kinda is. You can replace this thing without much fear.

Cowboy Hat

Defence: 12
Location: Hotland
Buy / Sell Price: 350 gold; 100 gold

Bought at Bratty and Catty's shop outside the MTT Resort, the Cowboy Hat is a good choice for people taking the Genocide route, as it bumps your attack stat by 5. You can get it for free when playing Genocide, too, which is doubly sweet.

Heart Locket

Defence: 15
Location: New Home
Buy / Sell Price: None; 250 gold

 The best armour you'll find on an average run. You'll find the Heart Locket in Asgore's home on Neutral and Pacifist runs. It's good.

temy armor

 Defence: 20
Location: Waterfall
Buy / Sell Price: 9,999 gold; 500 gold

The best armour in the game. The temy armor has fiendishly high defence, raises your attack, recovers HP every other turn, and increases the amount of time spent invincible whenever you get hit. Wear this and the rest of the game should be pretty easy. You can only get the temy armor buy sending the Temmie vendor in the Temmie Village to college (1,000 gold) and then buying it from him. The starting price is sad, but it comes down every time you die.

The Locket

 Defence: 99
Location: New Home
Buy / Sell Price: ---

Okay, this is the best armour in the game, but it's pointlessly strong. You'll only get it in a Genocide run, while looking through Asgore's house. Normally there's a Heart Locket here instead.

 Restorative Items

Abandoned Quiche

 Effects: Restores 34 HP
Location: Waterfall
Buy / Sell Price: None; 76 gold

Alas, poor Quiche. You can find the Abandoned Quiche by arranging the first set of Bridge Seeds to create a path along the water to the south. It's under a bench.

 Astronaut Food

 Effects: Restores 21 HP
Location: Waterfall
Buy / Sell Price: None; 25 gold

Another freebie healing item. You'll find a cooler full of Astronaut Food (well, two of them) in the garbage dump of Waterfall, just before you fight the Mad Dummy. It's of limited quantity, and it won't be useful forever, but it's a great resource for Waterfall itself.

Bad Memory

 Effects: Subtracts one HP or heals you to max if you only have one HP left
Location: True Lab
Buy / Sell Price: None; 300 gold

Why would you want this? You get Bad Memories from Memory Heads, the weird amalgam creatures you'll encounter first in the True Lab. They'll put one in your inventory if you select Item as an Action.

 Bandage

Effects: Restores 10 HP
Location: The Ruins
Buy / Sell Price: None; 150 gold

The first healing item you'll receive. You get it so early that it's actually considered a piece of equipment, at least until you equip something else. As far as I can tell it doesn't actually provide any defensive bonus.

Bisicle

Effects: Restores 11 HP; can be used twice
Location: Snowdin
Buy / Sell Price: 15 gold; 5 gold

Seemingly a dynamic restorative item, the Bisicle isn't that great overall. Sure, you can use it twice, but that means you have to waste two turns to get the full effect. By the time you leave Snowdin it won't be very useful - which is bad, since you get it at the end of Snowdin. Shrug?

Butterscotch Pie

Effects: Fully restores health; lowers Asgore's attack and defence if used during the battle
Location: The Ruins
Buy / Sell Price: None; 180 gold

One of the best healing items in the game. You'll receive the game's single piece of Pie by sleeping in your room at Toriel's home in the Ruins. It's a good idea to save this for fighting Asgore if you're on a Pacifist run, as it will hobble him for the entire fight.

Cinnamon Bun

Effects: Restores 22 HP
Location: Snowdin
Buy / Sell Price: 25 gold; 8 gold

A simple restorative item, purchased in Snowdin. One of the better healing items on a Pacifist run, but it normally loses usefulness once you gain access to later shops. You can trade a Cinnamon Bun to one of the tenants of the MTT Resort for 99 gold. Not bad, not bad.

Crab Apple

 Effects: Restores 18 HP
Location: Waterfall
Buy / Sell Price: 25 gold; 5 gold

Restoration! Not really worth the price, assuming you can avoid running out of Astronaut Food.

Glamburger

Effects: Restores 27 HP
Location: Hotland
Buy / Sell Price: 120 gold; 15 gold

No! Found at the MTT Resort's burger shop. Though it's an okay healing item, the Glamburger is pretty expensive. Buy one or two to use against Mettaton EX for boosting ratings. Otherwise, save your cash for something else.

Hot Cat

 Effects: Restores 21 HP
Location: Hotland
Buy / Sell Price: 30 gold; 11 gold

Eat the cats! Every now and then when you purchase a Hot Dog...? from Sans you'll get this instead. It's ever so slightly better.

Hot Dog...?

Effects: Restores 20 HP
Location: Hotland
Buy / Sell Price: 30 gold; 10 gold

It... might be healthy? Hot Dogs are purchased from Sans roughly halfway through Hotland's outer section, not long after Mettaton's cooking show bit. If you killed Papyrus Sans will not be at his post, and you won't be able to buy Hot Dogs. He'll also disappear after you reach the MTT Resort. Give a Hot Dog to the mysterious person at the end of the hall in the MTT Resort and he / she will give you a Hush Puppy, which is much better.

Hush Puppy

 Effects: Restores 65 HP
Location: Hotland
Buy / Sell Price: None; 150 gold

Well that's weird. If you take a Hot Dog...? to the MTT Resort and slide it under the last door in the east wing you'll receive one of these. They're great items, given the value added on top of the Hot Dog's healing. They're also great for selling, since you make a profit of 120 gold off each one, though Sans disappears from his Hot Dog stand once you reach MTT Resort.

Instant Noodles

 Effects: Fully restores health
Location: Hotland
Buy / Sell Price: None; 50 gold

Yum, fridge goodness. You can find the game's one and only Instant Noodles in Alphys' refrigerator, in the Lab.

Junk Food

Effects: Restores 17 HP
Location: Hotland
Buy / Sell Price: 25 gold; 1 gold

Not the best. You'll find these at Bratty and Catty's shop, beside the MTT Resort. You'll get more value out of Hot Dogs...? or Cinnamon Buns.

Last Dream

 Effects: Restores 12 HP
Location: See below
Buy / Sell Price: None; 250 gold

An unending supply of healing! Last Dreams only appear when you use the Dream Action during the battle with Asriel at the veeeeeery end of a Pacifist run. Every empty slot in your inventory will be filled with the things. They can help you get through what is, regardless, a fairly scripted battle. They'll remain in your inventory as 'Dreams' after the fight, and can be sold for quite a tidy sum, but by that point you don't need 'em anymore anyway.

Legendary Hero

Effects: Restores 40 HP, increases attack power
Location: Hotland
Buy / Sell Price: 300 gold; 40 gold

Really super expensive! For one a one-use item the Legendary Hero is not a great idea, even if it does boost your attack. You don't often need to boost your attack this much. Save your money. (It also boosts ratings during the Mettaton EX fight, like the other items you can buy from MTT Resort, but you don't need them that badly.)

Monster Candy

Effects: Restores 10 HP
Location: The Ruins
Buy / Sell Price: None; 25 gold

An early healing item. There are, as far as I know, only four in the game, all found early in the Ruins.

Nice Cream

Effects: Restores 15 HP
Location: Snowdin, Waterfall, Hotland
Buy / Sell Price: 15 gold (Snowdin) or 25 gold (Waterfall) or 12 gold (Hotland); 2 gold

A common restorative item. You can get Nice Cream from the Nice Cream Vendor, a blueish dude who travels between the regions. It's okay early on, but quickly gets outclassed. Note that if you befriend the two Royal Guards in Hotland they will buy all of his Nice Cream, and you'll be all outta luck.

Popato Chisps

 Effects: Restores 13 HP
Location: True Lab
Buy / Sell Price: 25 gold; 35 gold

Salty. You can purchase Popato Chisps from the vending machine in the 'lobby' of the True Lab. They're good for that area if you're in desperate need of healing during a battle with an Amalgamate, but they're otherwise kinda useless.

Sea Tea

 Effects: Restores 10 HP; increases movement speed in battle
Location: Waterfall
Buy / Sell Price: 18 gold; 5 gold

A restorative item with a twist. Sea Tea increases your heart's movement speed, allowing you to dodge attacks more ably. It's useful so long as moving quickly is a good thing, which isn't always true in battle. I personally prefer not using them. You can trade a Sea Tea to one of the residents of the MTT Resort for 99 gold.

Snail Pie

 Effects: Restores ? HP
Location: The Ruins
Buy / Sell Price: ---

If you decide to play Hard Mode in the Ruins at the beginning of a new game of Undertale, Toriel will leave a slice of this in your room instead of the Butterscotch Pie. Ew.

Snowman Piece

Effects: Restores 45 HP
Location: Snowdin
Buy / Sell Price: None; 40 gold

One of the better healing items. During Neutral and Pacifist runs you'll receive a Snowman Piece from the snowman in Snowdin. He'll ask you to take it with you on your journey, and if you return to him with it in your inventory during the farewell sequence he'll be contented. You will receive three of these during the Genocide run, because you're a monster.

Spider Cider

 Effects: Restores 24 HP
Location: The Ruins, Hotland
Buy / Sell Price: 18 gold (Ruins) or 9,999 gold (Hotland); 60 gold

Made of, for, and by spiders, in a joint Ruins and Hotland bake sale. Not terribly economic, and therefore not really worth getting, though Spider Cider can be used to instantly end the battle with Muffet. 

Spider Donut

Effects: Restores 12 HP
Location: The Ruins, Hotland
Buy / Sell Price: 7 gold (Ruins) or 9,999 gold (Hotland); 30 gold

Also made of, for, and by spiders, in a joint Ruins and Hotland bake sale. A better choice over the Spider Cider if you plan to use it for a quick defeat of Muffet later in the game.

Starfait

Effects: Restores 14 HP
Location: Hotland
Buy / Sell Price: 60 gold; 10 gold

Super expensive! Bought in MTT Resort, the Starfait is a ripoff for what it does. The only reason to buy these is to use them in the battle against Mettaton EX, as they boost ratings.

 Steak in the Shape of Mettaton's Face

Effects: Restores 60 HP
Location: Hotland
Buy / Sell Price: 500 gold; 14 gold

Whoa. That's stupid expensive. Don't spend the money. Like the other MTT Resort items the Steak will boost Mettaton EX's ratings - gee, I wonder why - but you're much better off saving up for something else. You can only buy one of these.

Temmie Flakes

Effects: Restores 2 HP
Location: Waterfall
Buy / Sell Price: 1 gold - 20 gold; 2 gold

... great. You can purchase these useless bits of confetti from the Temmie Village. There are three prices, but they all seem to do exactly the same thing, which is 'not much'. (You can make a profit by purchasing the one gold Temmie Flakes and selling them back, but... my god would that take a long time.) You can give Temmie Flakes to Temmies in battle, but... doing so... doesn't get you anything, really... just don't bother buying these, 'kay?

 Key Items / Miscellaneous Stuff

 Annoying Dog

Location: Waterfall
Buy / Sell Price: None

Yep. Exactly what it sounds like. You'll get the Annoying Dog when you try to pick up the artifact in Waterfall, though it will only remain in your inventory so long as you stay in the room where you got it. Using it will trigger a really weird scene, as well as get you some Dog Residue.

Cell Phone

Location: The Ruins
Buy / Sell Price: ---

A phone. Toriel gives it to you early in the Ruins. You can use the Cell Phone to call people, though you'll only get much use of it if you allow a few of the area bosses (specifically Papyrus and Undyne) to live. Alphys later upgrades the Cell Phone, allowing you to access your Boxes and retrieve items without the need for a physical box.

Dog Residue

Location: Waterfall
Buy / Sell Price: None; between 1 and 8 gold

Who knows what this is. You'll get Dog Residue after trying to pick up the artifact in Waterfall. Dog Residue doesn't do anything other than generate more Dog Residue. Stupid, really, but you can sell it endlessly. (Just be careful not to sell all of it, because you can't get it back once you run out.)

When you're selling Dog Residue it will appear as either 'DogResidu' or 'DogSalad'. DogSalad will earn you more, and you can occasionally gouge the Temmie vendor for a little extra. DogSalad can also restore your health... but if you try to use it, it won't divide. The only way to tell the difference between the two is to talk to the Temmie vendor.

Mystery Key

Location: Hotland
Buy / Sell Price: 600 gold; can't sell

Oooo, how mysterious. You'll receive the Mystery Key from Bratty and Catty near the MTT Resort. It allows you to open the colourful house next to Napstablook's in Waterfall. You won't find anything of practical use inside, but there are lots of diaries to read that will fill in the backstory of one of Undertale's more interesting characters.

Punch Card

Location: Waterfall
Buy / Sell Price: 25 gold (15 gold with an umbrella);

Ooo, a freebie. Punch Cards are normally used to earn free Nice Creams from the Nice Cream vendor in Waterfall. Buy a Nice Cream, get a Punch Card. Submit three, get a free Nice Cream. It's wiser to keep the things, however, as you can use them as one-shot items to make your punches stronger during a fight. These are no longer available after you complete Waterfall, as the vendor packs up and leaves for Hotland.

Undyne's Letter

Location: Snowdin
Buy / Sell Price: ---

You'll receive Undyne's Letter after beating Asgore on a Pacifist run and talking to her in Snowdin. She asks you to deliver it to Dr. Alphys. Do so and you'll trigger the events leading up to the True Lab. If you decide to throw this away, for whatever reason, you can return to Undyne and receive...

Undyne's Letter EX

Location: Snowdin
Buy / Sell Price: ---

Undyne's second letter to Dr. Alphys, assuming you threw the first away. You cannot throw this one away, try as you might, and why would you bother anyway?

Main Walkthrough