Word scrambles are pretty fun to solve, either by individuals or by teams.

It might require some work, but you might be able to come up with some kind of trivia game based on word knowledge. "What does the prefix 'macro-' mean?" (You could probably cull some interesting stuff from the AWAD archives.)

You might also consider bringing different types of board games (scrabble, boggle) and letting some of them break off into groups of 2 or 3.

Also, consider just having a fun time to share some favorite reading material. There's this hilarious bit of a short story in Pinker's "How the Mind Works" about how "meat can think" that I think 13 year olds might be able to appreciate. Pinker says he got this off the internet some years ago, but I've never been able to locate it. Anyway you start off with something like that maybe (or whatever you find funny) and then ask them in turn if there's anything they've read that was particularly funny. Of course, this would have to be planned in advance so those who wanted to contribute would bring their books.

Maybe just a short period where people discuss books - instead of reading them real time.

good luck,
k