These are items that are designated as "usable" in the item description and can be used from your inventory. Using an item will generally cause it to be expended. Some items produce new items, some affect you, others give or take away meat, etc. Some are maps, scrolls, familiars, or books. Familiar Hatchlings can also be used from inventory even though they aren't specifically designated as usable. Gift Packages behave in a similar way, although they are opened rather than being used.
