Took me forever to figure it out myself, but you have to go up from the cave the kids who stole the beer are hiding and push the small board off the hill. Don't push it straight down onto the boxes though, first push it to the left a few feet and then push it down so that you can push it forward to the set of boxes the wrench is on. It might take a few tries if you move the board to the wrong spot, but that's how you get it.