Treasure chest key
From A KoL Wiki
I don't know why pirates would bother to lock their treasure chests anyway. Burying them in a secret location you need to solve a map full of riddles to find seems like plenty of security, and it's not like someone's gonna dig up the chest and say "Aw shucks, it's locked, guess we're out of luck, boys."
Type: accessory
Cannot be traded or discarded
Quest Item+30% Item Drops from Monsters
+30% Meat from Monsters
(In-game plural not known - currently impossible to determine.)