What item classes don't take up inventory space?

In Kingdoms of Amalur, you've got a finite inventory. However, I've noticed that not every item (such as alchemical reagents) do not count against your limit.

What item classes are effectively "free", and don't take up space in your inventory?

Crafting ingredients/parts/reagents and keys all go into special bags just for holding them, so they do not count against your inventory (I don't know the upper limit for those offhand, probably 100). I don't know if the craftables bags take up space. Everything else, from notes to swords of bludgeoning do count against the limit. You can have stacks of an item and it will only count as one slot in your inventory (e.g. potions).

Note that to pick up a potion that you already have, you need at least 1 slot free. I think the game goes and puts a stackable into a free slot first, then goes and moves it into the relevant stack instead of just putting it in the stack first. The stack limit for potions and for most other stackables seems to be 10. Lockpicks go to 99, I think the same for repeatable quest items like Freeman Armbands.

If you've stolen a stackable item, it will go into it's own pile, and won't be disbanded until you use up the stack marked stolen. If you have a full stack, then new items will be put into the next stack, which can be the stolen stack. You can end up with 2 incomplete stacks this way.

Quest items will not count against bag space. Everything past a 10 stack does except for regaents, crafting items (crystals and blacksmith), and keys. Keys are practically quest items. Near the end of the game I am averaging about 70 items. Some items cannot be destroyed or stored but DO count against your space. So, pick up backpacks every chance you get. You also cannot craft backpacks. That have to be purchased.