From the Super Mario Wiki
Retrieved from "https://www.mariowiki.com/index.php?title=Wooden_chest&oldid=2390742"
They can be forced open by any attack and reveal their contents upon doing so. As their wooden appearance compared to their metal counterparts indicates, rather than containing a treasure, wooden chests contain more common items like garlic, a Smiley Bomb, or coins. When Wario re-enters a wooden or a steel trapdoor after having completed the sub-level inside, he finds a wooden chest with coins in it where the red diamond used to be.