I allow myself to be a little more free with my calories on the weekends, but I try not to go crazy. Then, during the week I try to get back to what works, eating healthy and exercise. I do try to keep up with exercise on the weekends also, but sometimes with all of the other things that I need to do it's impossible. If I over eat too much now I will feel really sick, so it's getting easier not to over eat.
I hate those parties also, and have found that if it is a take your own piece kind of thing I'll take half a piece of cake, or if it's something that's offered and I really don't want to go over my cals for the day I'll say, "I just ate before we came, so I'm really not hungry," and usually that's true, I'll eat something better for me so I'm not starving and drooling over goodies.
Now that it sounds like you've got your plan figured out, I'm sure those days will be few and far between. Good luck!!
Goal 3: 125 whenever I get there
Goal 2(restart): 130 by May 25th (2013 vacation)
Goal 1: 135 by May 24th (2012)~~~~Accomplished!