Soulbound shulker, but you can only place in soulbound items inside: Purpose, have safely all your voter items or promos in hand whenever you need 'em
It's a good idea but I never carry that many soulbound items around. I think a better idea would be a soulbound shulker that has a few usable slots that could hold anything.
the question would be, would you use these soulbound items, if you had them with you? but fair enough, although I think that would be a bit too op.
Maybe but not enough items to make use of all the slots. Having a soulbound shulker with just 3 slots would be of more use because players could store an elytra, food and rockets to be used in case of death and you don't have enough time to run back to the point of death before the items despawn. I had that happen to me twice.