I'm talking about RPG mechanics, specifically about items which are commonly called powerups in arcade games.
Once your character picks up these special usable items, they don't go in the inventory slot, but instead are immediately used.
A notable example is the Prince of Persia potions which, when drunk, give your prince more hearts (permanently increases total health).
How are these items called? Does "powerups" suffice? How about the negative items? "powerdowns?"