Wow, a lot of good choices here... Enjoy the chance to show some slack to some who may be unfamiliar with slack key...perhaps don't go exploring TOO far for a final... Is it low key and a comfortable place to share? Are there "Monsters"? I so, show them some joy.
But KISS...do something either you're familiar with or are confident and passionate about-- and if you go with something new-- you can learn in short order. How necessary is it to stretch yourself on this? Do something you enjoy, sounds neat, and makes the others say, "Tell me more, play me some more".
Sometimes people playing/learning "serious" stuff forget about the simpler joys in music. Give em a taste! Good Luck. Let us know how it goes.