I think it would be fun to disguise items' looks one way or another, like making a potion of harming look like a golden apple, making a spell book look like a twig etc.
Alternatively, if no item is used to disguise something, it could become invisible.
The change would only apply to non-placeable items and would be cosmetic only, changing the item's sprite to that of another.
Perhaps Sense Magic could make a player see the true form of items.