I don't know how crazy you want to go with the decorations, but you can buy the giant standees of the characters from the Wizard of Oz that can stand up on the floor. You can purchase real cornstalks or the cut out kind. You can have cut out scarecrows hanging up. You can have volunteers dress up like the characters from the movie. Just do a search on the internet, and you will be overwhelmed with ideas for your auction. Good luck!