Halloween?!?!

At my school, I'm in band. I 'play' clarinet (well...I can make noise out of it....) Anyway, in October, my town (my very, very SMALL town) has a Halloween parade. The band always performs in the parade on a float or something, and our band director says we HAVE to have a costume. Now,unfortunately I can't go trick or treating this year (GRRR!) even though I really want to, so I didn't think I was going to need a costume. And so now the parade is coming up and I have NO FUCKING IDEA what the FUCK I am going to be.....help please ?!?! and if u guys can think of any ideas where the costume will keep me at least slightly warm considering how friggen cold it gets here in October, especially at night (which sucks.)
However, the cold and the lack of trick or treating this year still does not get rid of the fact that Halloween is my absolute FAVORITE FUCKING HOLIDAY.
So anyway, yeah. Could you guys help me think of a costume for my Halloween parade? Thanks!!!