#RolePlayingGame #RPG mechanic idea:
Characters' base MP is rather low, but certain items (call them “energy crystals” or whatever) increase max MP (and maybe change spell behavior) while in the character's inventory.
One can get quite powerful by carrying a lot of them, but that leaves no room for loot.
Characters with especially low MP (warriors and whatnot) can also carry a few of these to cast the occasional utility spell despite their lack of skill.
Sound like fun?