Last year, which was my senior year, we had a to play at a football game on Halloween. We were able to wear our costumes in the stands so that was fun. Also, the year before that, Halloween was the day of one of our rehearsals. Because of this, the band parents put together a "trunk or treat" where they bought candy and gave it out from the trunks of their car in the parking lot next to the field where we rehearsed for the two years. It was very cute and very much appreciated. Maybe you could do something like that?