upgrades for buffs would be cool, like a one-time upgrade that made dice roll again on a bad roll, or for clovers to add a chance to activate chance-based effects twice. Donuts could receive a chance to make a weapon attack an extra time. all of these could require 3 of said buff.
a legendary that upgrades the ability of the weapon it is put on, knife giving every weapon after a chance to crit or 15% increased damage, banana give non bananas an extra attack. ect...