Here are a few traditional ideas: hobo, ghost, ghost of a hobo, pirate, pirate's best friend, pirate's wooden leg, pirate's original dismembered leg, gay pirate (Elk may still have his costume you could borrow), nun, priest, altar boy, parishoner, bishop, pope, Martin Luther (not recommended if you're catholic), dog, cat, geeze, I could go on and on.
I'm going as a motocrosser this year. I don't suppose that'd win you any contest though, huh. How 'bout a trials rider? I bet no one else shows up as a desert racer. Unless one of them reads this forum, then I guess I just ruined the idea.