Have a "drive in movie" with parents tailgaiting ahead of time and then bringing lawn chairs for a movie outside!
A tailgate - block party type gathering sounds fun too.

Our HS has a huge tailgating party before a specific football game during the year and they get a huge response. Maybe you can have an event that it leads up to.

Has anyone done this for a family actiivity? We were thinking about having the families park their cars and put the tailgate open and eat and be social...the other option is to have it around Halloween and the kid could go and trick or treat between cars and the kids could dress up and such...any ideas?