I'm not sure if anybody has posted this before, but I know kids in general LOVE these marshmallow guns:http://pad39a.com/gene/mgi.html
What about making personalized monster stickers that they could stick on bike helmets? Or those reflective bands for their arms or ankles when they ride their bikes?
Water bottle holders? Hey, the kid must get thirsty even when he's playing video games.
Tote bags stenciled with "boy" friendly art? - drawstring bags with extra long string so that they can wear them as backpacks?
If all else fails, how about a bunch of quarters and a trip to the arcade?