Here is a short list of a few things you can do to reduce the number of calories consumed tomorrow.
1) Evaluate which foods you'll enjoy the most, and enjoy just those foods.
It's not that I dislike mash potatoes, pecan pie, wine, etc...I just don't like them enough to waste calories on them. Instead, I'm going to invest in the things that I really like. For me that's stuff like white meat turkey, dressing, homemade cranberry sauce, etc.
2) Snack before the big meal
It's a good idea to have a balanced snack about 3 hours before your Thanksgiving meal. Fruit, vegetables, nuts, seeds, low-fat dairy-high protein like greek yogurt, and/or a protein supplement/bar would all be great choices.
3) How important is dessert/alcohol to you?
In some cases, your dessert/alcohol could account for 25%-50% of your total calories consumed on turkey day. With desserts like pecan pie and cheese cake ranging between 650-1000 calories per slice, you might ask yourself..."do I like dessert that much." Same goes for alcoholic beverages. Two glasses of wine would run you roughly 270 calories...drink water instead of wine/beer and you've got an extra 270 calories to "invest" in another area.