In my "real" job I teach History to high schoolers. If you're at GenCon this week I'll also be doing a lot of the Boot Camp scenarios, so my advice that I'll share here comes with a heavy dose of experience from both of those. So here goes:
1: Keep it simple. Play on the beginning maps, ideally, ones without water. We teach Boot Camp with only trees. We don't even introduce hills there. Your job in a demo is to show how basic game play, not the entire rulebook.
2: Keep it small. The mechs that we use in Boot Camp are small and simple. They are both light mechs. They are intro tech. They share one weapon system, but they do have a second, different, weapon from each other. They do not have minimum range. In short, there's not a whole lot to understand on them.
3: Keep it short. Boot camp is taught on one mapsheet with each player having one mech. They will fight each other quickly. They will learn the game. There's nothing gained by giving them a lance and putting them on a 3x3 set of maps to duke it out with seven other people. It will overwhelm them.
Beyond that, you've covered a lot of the other basics: have supplies plentiful and ready. Have product visible for players to ask about. Good luck!
