Another item idea, a very simply one at that:
Wastepaper, as found in Chibi-Robo.
Basically, it's just scraps of paper lying around on the ground. You can pick them up an throw them at people for minor damage. When they hit a person, they explode in shreds of paper. Very simple item.
The one unique attribute of them is sometimes when they explode, they'll instead explode with stickers flying out, which can be collected of course.
And also, the
Bull Cap from both the original Wario Land and Virtual Boy Wario Land:
Basically imagine the above pith helmet with spikes.
Wearing the Bull Cap grants you increased power, and one unique ability; if you jump towards a ceiling while wearing the Bull Cap, the horns will stick into the ceiling and you will hang from it. You can then jump down from your spot and use your attacks or jump again. This makes this item extremely useful for recovery, especially under stages like Battlefield.