A.R.
Depending on how much you want to spend....
Are they interested in learning to play an instrument? You could give an instrument and lessons.
How about other clubs/memberships? Like park district classes or YMCA membership so they can swim/play in the gym/etc?
Art supplies are good if they like things like that, or how about items to redecorate their rooms? Would they like an aquarium with fish or a turtle, etc?
Are they into science? How about a microscope or telescope? An ant farm? They sell those National Geographic kits in Walmart now and you could include a homemade "promise" coupon to take them to a museum or planetarium....
Just a few random ideas!
Amanda