Like Support Skills, Usable Battle Items have no failure chance, but do have individual effects that may fail. For example, Crow Bar is not guaranteed to Cure Blind.
EXP Food is used in your Camp>Creatures menu and Camp>Quick Action menu as an EXP resource for hungry creatures.
This process can be partially automated with the Feeding Bowl, and hasted with the Feeding Trough and All You Can Eat Sign Key Items.
Smithing Items are various alloys and oddities that can be used to enhance your existing equipment in the Skyfire Forge Smithing Shop in Onyx City 2.
Breeding items are used to enhance or change the breeding results of your various creatures.
They can offer good beneficial effects like a higher superb chance, neutral like more creatures added to the pool of possibilities, or negative like a failure chance.
Note that negative affects are always accompanied by powerful positive ones.
Tattoo items usually enhance the style of your creatures and often offer other statistical benefits or hindrances as well. You can read more about tattooing here and view the complete Tattoo list there.
Consists of miscellaneous items that tend to have more unique uses throughout the game.
Cooking items are only used in Le Chef's shop in Onyx City and some Alchemy Shop recipes. You can read more about cooking here.
Building items can be used to craft new equipment in Orion's Equip Building Shop.
Creature Gifts contain random quality eggs and can be opened within your item menu to receive various eggs.
If you do not enter a number in the input field where "selling" is mentioned, the Open button it will default to opening at least 10 at a time. This amount can be further increased with the help of the Clown Arm.
Alchemy items are used almost exclusively for Cthulhu's Alchemy Shop in Onyx City 2.
Gene items offer assistance during Genetic Recombination, a way to give your creatures unique traits that are auto generated for them at birth in Harry Shipman's Shop.
You can read more about Genes here.
Dungeon items offer generous benefits to your usual grinding by offering more coins, items, eggs or other things.
Enchanting Items influence the Enchantments on equipment, whether its providing access to certain types of enchantments or increasing the chance of particularly good ones.
Painting items increase the chance of a successful egg painting in Poptin's Egg Painting Shop.
Please note that even with these items aiding you the chance of success is extremely low.
Loot Boxes are opened similarly to Creature Gifts, but Loot Boxes offer various rewards other than eggs.
You can never be quite sure what you'll get! The vast majority of these produced daily by LESPs.
Blood Supply items contribute kill credit to your Player>Books>Blood Diary without the need to grind monsters.
The creature blood you receive will be random however, belonging to certain categories dictated by the items.
Evolution Items are dropped by Pocket Nightmares and evolve them. Please note that while all Pocket Nightmares have a unique item, not all of them can evolve, and there's no guarantee they will later.
Feel free to sell the ones you don't need while taking that into consideration.
Nifleball Items can be crafted with Pocket Nightmare Evolution items, lesser Nifleballs and other items.
They're usually good for hunting particular forms of Pocket Nightmares, so you can optimize for First Superb Hunts or general hunting with them.
Rebirth Items enhance rebirthing actions, usually giving you a chance to double up within a certain range.
You can read more about Rebirthing here.