Here's some quick tips and a workout that can help you keep up with your fitness goals and not miss out on time with the fam.
Keep in mind the key here is portion control. For the average 20-something this might be hard because you know you don't eat like this when you're at college or off living on your own,but it's do-able.

1) Grains not carbs. You may or may not have any control on what is served at your Thanksgiving feast, but if you have the opportunity opt for whole grains wherever you see them. Whole grain foods have tons of good fiber that your body needs and are good for you. There are tons of recipes out there for whole grain stuffing or less traditional but equally awesome whole grain rice dishes.
2) Veggies. Thanksgiving is the mother of all veggie holidays so go ahead and load up. Even if they're covered in cheese or whatever,
veggies will still be better for you that loading up on mashed potatoes or straight starches that even the most vigorous of post-meal walks won't take care of.

3) Protein! Turkey is a great source of protein, and as long as it's not been deep fried should be a about as healthy as you'll find on the table. Make sure to cut away the fatty bits while they're on your plate, if there are any, so you don't have to work extra hard to cut those off yourself later.
Lastly, try to get in some physical activity either before or after the big meal to help burn some calories for the big day, and definitely try to get back to your usual work out routine ASAP after the holiday festivities have calmed back down to normal.
Here's a great work out I found to help tone your core that you can do while still being in the same room as the big games you're sure to be watching.
Enjoy the holiday and keep loving life's IOI's as they come!