This is a hard one! I am a big gamer too, and can't think of anything that wouldn't take an expert to do. :mrgreen:
If he plays pencil-and-paper games, you could go with a dice bag, maybe? If he plays medieval-setting games (like D&D), I could think of some things, especially accessory-wise. :think: I have seen a chart for runic letters. They were designed for fair-isle, but you could do them in a stockinette and purl pattern stitch. A runic scarf?