Remember: Fizzy water + 1 shot hard alcohol of choice = 80 calorie drink.
Limit yourself to that one (or two tops), and DON'T YOU STOP DANCING.

I second the food advice already mentioned, although I wouldn't eat a big dinner beforehand (save some calories!). Remind yourself to have ABSOLUTELY NO FOOD there except the healthy things you brought and (1) the alcohol will have a stronger impact; (2) you won't go over your allowance.
I find I lose more on weeks I go out, because I dance so much. Seriously aerobic workout. And even if you do go off-plan, don't worry -- you can just work it off the next day. Have fun!