This is from my own project. It is an outdated and incomplete list but it might help you out.
I advise you to create families so you can browse items in your game with filters, assuming you are including a large diversity of item types.
https://www.dropbox.com/s/o60bqj7ghdaa71m/Item%20List.jpg
Thanks, I think I have nearly all of those ones now.
I think it's always best to start out brain storming lists.
Things in a game are not real things, they are just signs of things.
If I find a skull in a game, it's not really a skull. It won't break if I drop it. My character won't be creeped out about touching it. It won't decompose. I can't get DNA from the teeth.
Actually it's more likely to be a key, or an ingredient or a junk item or a bonus item or even food. It could be any of these and any of these usages could easily use something other than a skull to represent themselves.
Some things lend themselves better to a particular use than others however. A sword is most often a weapon, a knife sometimes a weapon or sometimes a tool. A jewel is usually a treasure item, but may easily be a puzzle item, required to solve a particular puzzle. The semiotic relationship between signifier (visible in game object) and signified (the function of that object) is pretty loose in games. This is especially so in ASCII roguelikes where @ is a player and % could be an item and "G" could be a giant or a goblin or a gargoyle.
Sometimes there is a particular mechanical link that fixes how an item must be used. For example, the belt might need to be "worn" before you get any use out of it. A potion needs a certain key press to "drink" it. But in many cases the difference between two items is almost unimportant. If you don't have drinking restrictions or item damage then scrolls and potions are nearly the same. They both start out unidentified and trigger an magical effect when used. Scrolls might require a special skill to read, or not.
How the designer decides to separate the usage of various items is up to them, but once you start introducing mechanical limitations to an object then it needs to be a separate class.
One game might have
magical_items(scrolls, potions, wands, etc..)
Where each is activated by the use item action and any potion can have the same sort of magical effects as any scroll or wand, and there is no item damage (like your scrolls being damaged in fire or water)
another game might have
scrolls()
potions()
wands()
etc..()
Where there are restrictions on what kind of magical effects each item class can have, their might be different actions for using each type and each type might have other restrictions.
But before you decide on those things you need a pool of possible themed item types so you can draw from them. You don't have to use everything on the list, but it's good to have a list to start with. Same with monsters, skills, spells and everything else.
Many items have restrictions of convention inherited from the roguelike genre, but it's really OK to break these conventions if you feel the reward of fresh game play is worth the risk of confusing players who are used to a certain convention. If the usage of an item is not clear and there isn't any help to describe how to use it you could end up with a useless item.
