A silly activity good for all ages. This will have everyone laughing hysterically by the end. The key, though, is to keep the actual activity a secret until you start it.
The campers all bring in two brownies. They can buy them, make them, etc. The key is that they DO NOT KNOW what the brownies are for. Your staff can bring brownies too, but probably not necessary. Let the anticipation of the “activity” build throughout the day leaving the kids and possibly even the staff to wonder what they are doing with those “sticky” brownies.
The activity is that the kids smash one of their brownies on their forehead. They then see how many times they can jump up and down before the brownie falls off. The winner is the one that takes the most jumps before their brownie falls off. This is hilarious, and a great photo opportunity!
Oh, and the other brownie is for them to eat. Usually you will get lucky and some of the kids will bring in a whole pan of brownies so counselors will get one!
This is better done outdoors in the grass.