- I eat before I arrive.
This is a very commonly suggested strategy.
- I don't eat when I'm not hungry.
Corollary to the above. It's become much easier for me to avoid snacking on party foods simply out of boredom or politeness, since I now experience actual pain in my stomach when I eat too much.
- I don't eat anything that I know or suspect contains animal products (other than honey).
This is because I'm vegan primarily for reasons other than health. I only intentionally violated this rule once this year, due to poor planning and great hunger, and felt really bad about it. In any event, this eliminates the majority of foods at most parties.
- I keep on running.
It's been hard to run in this chilly, windy weather, but I gotta do it. It's not so much the calories burned from each exercise session (running burns roughly 100 calories per mile, and I've been running around 20-30 miles per week). It's the metabolism-boosting effects of the aerobic effort that help me burn more calories all day long, especially when I run in the morning as I usually do.
These strategies certainly aren't appropriate for everyone, but they're working well for me.