Twilight Sparkle and make a plan:
1) Get a smaller plate if possible.
That way you physically can't eat as much in one sitting. This lengthens the time you are eating food, so you get fuller faster. Scientific fact! Anyone who has ever eaten at a dim sum restaurant or sushi boat place can testify to the longer meal = fuller faster = less consumed. Also the act of getting up and walking will help digest your food and so you won't have as many digestion issues.
2) Don't have second helpings.
This one is going to be tough, but remember if you don't eat it now, you can have it for leftovers! Now this might involve some preemptive saving for later, but if it is the dish you're bringing to the potluck, save some of it at home and bring the rest. What the host doesn't know can't hurt their feelings!
3) Stop when full. Thanksgiving is about being thankful for all the good in your life, like health, family, and friends, not for stuffing yourself until you burst. Now I know that a lot of us deal with the family that makes comments about our weight and then during these holiday gatherings are constantly shoving food on our plate. Be firm and tell them no. Again we live in a wonderful age of the refigerator and freezer. Any of this delicious food will actually taste better the next day!
So now I just wait and try to be EXTRA GOOD before T-Day.