Yipes! Have parachute pants come back yet? Acid washed jeans and a t-shirt with something "Awesome!" on it would probably work. Don't forget the headband!
I voted for Mrs. Pac-Man in the poll, but I'm not sure it's the best game. "E.T." has the cultural significance of being a symbol of the Crash (though I honestly don't think it's responsible, the great Landfill Legend is a telling sign of '80s overindulgent doom). Very poorly written third-party games for the Atari are probably more to blame, as well as some Atari Corp. management decisions. It would be nice to showcase a GREAT game on the 2600, something fun & graphically intriguing, but I'm not sure what that'd be. I wouldn't bother with "Combat", and "Warlords", while fun, is pretty simple (a PONG variation). Otherwise, "Yar's Revenge" is generally accepted as one of the best games and it's flashy. That way, you can communicate that the 2600 could've been a more competitive system had the market been different (if the market hadn't been glutted with crappy games, there might've been fewer but better games).