From the Super Mario Wiki
A Wooden Chest is a Treasure Chest of sorts found in the game Wario World. They appear as wooden containers with a square-shaped base and are edged in dark metal rims, giving them a rustic look. 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 one of Wario's Treasures, 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 minigame inside, he finds a Wooden Chest where the Red Diamond used to be.