It's kind of specific, but some clothing and hats sprites maybe?
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I think some clothing could be really versatile, like all three examples you mentioned. My current RPG/rogue-like is struggling for armour pick-ups--I'm thinking of using partially drawn-sprites, like the top half of sprite 53 in the democart with some palette-swaps could look sort of like a helmet, but it's a bit of a stretch. My first project with plumbers might have had a use for gloves, overalls, boots, as power-ups. :)