For example, hotkeying a potion or a book?

Could be with SKSE, just wondering if there are any mods that do this?

You should be able to hot key anything in your inventory.

I hotkey healing potions all the time. What will happen is if you use the items up, the hotkey goes unassigned. Perhaps this is what happens with books. Also, since books are a two step action, Read, then Take or Leave, perhaps the hotkeys can't work with those the same way.