Oh there are so many pranks to pull. It all depends on the severity and consequences/repercussions of your actions. Here are a few.

Put a chicken bullion cube in the shower head. I dont care what scent away soap they use he will smell like like wonton soup. Funny thing is they will take another shower to de-stink....

Habanero peppers or scotch bonnets work in a great deal of hilarity when slipped to the unsuspecting. Beware on this, paybacks are a real beeeeeacth.

Slip in a diuretic/water pill or 8 into the morning coffee. Works especially well when guys attempt to sit on stand all day......

Tear little holes into all the packages of handwarmers in your buds day pack - the night before he needs em.

Have fun. Laugh often at camp. These are indeed the times of your life.