My summer camps are pretty low key. I only run them on Tuesdays and Thursdays from 9 to 1. I do it at a campground and the first hour is a regular lesson but I also invite campers from the park to participate for $10. The next hour is filled with activities like obstical courses, frizbee, hacky sack, kickball, or in & out. Then there is another lesson followed by lunch. After lunch I'll cover one more lesson before we jog to the lake and spend the last hour swimming.
I'm not expecting to make tons of money doing it, it's just something extra to give kids something to do who don't usually go anywhere during the summer months. It also insures that my own kids get plenty of swim time each week.
For the last session, I hold a cook-out for all of the parents to join in. It's a great time to talk with the parents about anything, not just karate. I don't have a lot of time to talk to parents during regular classes because I'm at the Y and I'm the only instructor there. My classes run back to back so at the cook-out I get a chance to catch up with the parents and see what is going on with them.