It seems like you might need a Schelling meta-point as an injunction: no meta-gaming, or Munchkining, the Schelling point game. This could be important because lessons about coordination problems, and how to avoid them, seem valuable to people who attend meetups to ostensibly learn such lessons, and this is helped by not creating additional coordination problems.
That is, unless, the meetup group actually wants to learn about how they might want to act in peculiar game-theoretic scenarios, where players have information and signaling powers they wouldn't normally have, in which case, don't mind me.
"No abusing the rules" probably only works if people can coordinate successfully on "the spirit of the rules".
I think one direction to explore is to have a games master picking sets that are easy to define (at least roughly), but hard to enumerate. Things like "locations in New York", "subsets of the integers", "nonempty finite subsets of the irrational numbers", "letters in non-Roman alphabets", "man-made satellites currently orbiting Earth", "models of jet plane", "movie...
A month ago, a new type of thread was proposed: a monthly page for meetup reports. The idea is that meetup attendees, or organizers, who wanted to share information about how the meetup went could do so in the comments of this thread. This is so information is dispersed, but without the need for anyone, and/or everyone, to dedicate their own thread to the report. The idea worked for January, and nobody had objections. So, we'll do this every month.
If you had an interesting Less Wrong meetup recently, but don't have the time to write up a big report to post to Discussion, feel free to write a comment here. Even if it's just a couple lines about what you did and how people felt about it, it might encourage some people to attend meetups or start meetups in their area.
If you have the time, you can also describe what types of exercises you did, what worked and what didn't. This could help inspire meetups to try new things and improve themselves in various ways.
If you're inspired by what's posted below and want to organize a meetup, check out this page for some resources to get started! You can also check FrankAdamek's weekly post on meetups for the week