I have a 13-year-old son. Gift card, gift card, gift card. Toys r us or a game store would be great (assuming he has a game system, if not, toys r us is still good). My son LOVES getting gift cards. That way there are little things he needs that no one knows he needs and he can pick it out himself. Like the cordless xbox controller, that no one knew he needed...my son just bought that with a gift card.
I may not be able to lose 100 pounds, but I can lose 10 pounds 10 times!