i have an idea, a shop. which sells consumables and upgrades. the shop could be located inside the barrel.
the health restoring consumables could be anything from soda, to an eraser, to a razor or scissors.
for the upgrades my ideas are
faster reload/pumping:allows you to reload all guns faster as well as pump the shotgun faster. "you've got opposable thumbs, why don't you use them?"
piercing shots:shots pierce through a certain amount of enemies "maybe these bullets would be more effective if they weren't made out of styrofoam"
armor:allows you to take an extra hit "stylish!"
stronger bat:bat does more damage and knocks back enemies "aluminum. how robust!"
and those are my ideas. hope you like them.