We do a lot of free ads for Etsy craftspersons, yeah, but this is pretty good: Old school NES carts are available as mini-sized necklace charms, in hypoallergenic silver if you want to upgrade.
Artist Laura Swingle makes the charms; her page features Super Mario Bros./Duck Hunt, Zelda, Zelda II, Super Mario Bros. 2 and 3, Metroid, and Final Fantasy. She asks that you specify which game you want, but it's not clear if that's from the catalog photo, or from all available NES games. I'm thinking "PICK ANY GAME" means what it says. If you don't pick, she gives you SMB/Duck Hunt.
The charms are about the size of a penny - tasteful and inconspicuous, but great conversation pieces once they're noticed. $US12 gets you one, $US18 gives you the silver upgrade.