What is a good gift idea for my boyfriend?

I want to surprise him before he leaves for ten days...I'm just really bad at figure out what. Robert and I are both 16 and we've been together for almost 4 months. Normally when I surprise him with something, it's bringing him lunch to work or something simple like that. I'd like to actually get him something that will remind him of me on his trip. He plays football, likes the Broncos, and pretty much spends the rest of his time working hard or seeing me. I'm stuck on what can be sweet but also be something he'd like. Thanks for all the help =)