Jack is an imaginary person
Have several campers walk onto stage laughing, and then one says, “Hey, let’s toss Jack up in the air on the blanket!”
All the other campers surround the blanket and then start tossing ‘Jack’ into the air.
They throw him higher and higher 3 times. On the fourth time, they pretend that Jack doesn’t come down.
They ask each other where he is, then finally walk off the stage without Jack.
A few skits later they all run back yelling “JACK!!” and pretend to catch him.