I think you made a wise decision! I've been on Atkins since the end of April. Earlier this month, I went off the plan and essentially "carbo loaded". Boy was I sorry! And not because I was afrad of gaining weight or spiking blood sugar levels. I knew that was going to happen (but I did it anyway, go figure). Got the worst case of gas after a couple of hours that I've ever had in my entire life. It really, really hurt - could hardly move. Wouldn't wish it on my worst enemy, let alone my friends! I'm pretty sure I've permanently lost my desire for "carbo loading" and am resolved to do a better job of planning ahead.
If your body treats you the same, you will not be dancing (or at the very least you will "pay" for "cheating" big time that evening.
Nuts are a good snack to take along. They don't take much room and seem to satisfy you fairly well. Macadamias and almonds are my favorites. Also, eat plenty of good legal stuff before you go. Bet you will find that you don't even want the "bad" stuff. I've found that legal Atkins food keeps me satisfied a lot longer than the things I used to eat.
Anyway, I know this is too late for your Dance Festival today, but hope you had lots of fun and now know that it is possible to stay on Atkins even when you are away from your usual routine.