Great idea for a post. Unfortunately, there's no meetup in my area (Knoxville), and worse, there are very few aspiring rationalists to begin with. But I've often wished there were a meetup.

One thing that I've thought might be good at a meetup would be a game of Resistance.

The Wikipedia description probably provides a more concise and accurate description of the game than I could provide, so I'd recommend reading it if you'd like to understand my recommendation.

Because of the advantages over games like Mafia, Resistance becomes much more about game theory than about pure luck. It requires thinking on several levels, especially by the spies, who must choose whether or not they want to sabotage the mission, exposing themselves, or let it succeed, and let the resistance score a point. I haven't been in a position to play it too much, but when I have, it's always been good for rationalist training.