I've heard other events have a punch card (of some sort) and have all of the team members get them punched every hour (at different times and locations that is announced each hour) and then have everyone with COMPLETED cards turn them in at the end for a drawing...usually something BIG.  Keep them busy with new and exciting activities, fresh food vendors/items at various times, drawings/contests, performances, etc. going up to the Fight Back ceremony at the end.  Reward the team with the highest percentage of participants at the end?  Get a celebrity (local works, too) to come out and speak/present/perform?

 Just some thoughts!  Hope they help!

Anne