I am sure that you will get as many different suggestions as there are people.
This is one idea but I am sure you will get flooded with other great ideas too!
If it were me; I would try to minimize the exposure that I had to "bad" food. Eat the meal with your family and enjoy the company. Try to choose the foods that will fill you up that are the least damaging. I once heard that from an OA sponsor long ago. Sometimes, no matter how hard we try, we can't always stay on plan. Next best thing: do the best you can in the given circumstances. Drink lots of water, take smaller portions and chew really slow. If you have the self-control, either refuse dessert or take the smallest possible piece you can and then eat small pieces slowly so you won't wolf it down and then wonder where it went. Remember those days?
The next next best thing: do "damage control". Add more exercise while you are there. Go for a walk right after the meal is cleared from the table. Of course, if it is expected of you to help do the dishes do those first before your walk but the main thing is to get away from the food and all the good smells that linger.
Since you have the advantage of staying in a hotel you can do a couple of different things: schedule workouts at the hotel if it has a small work out center (most of the chains do), go for a swim or a walk around the property if you can.
Keep your expectations realistic. I think, if you have been following a plan long enough, some of this will be second-nature. The main thing is do your best. If you can't do your best, do your second best. And, whatever you do, don't beat yourself up about it. One week out of 52 will not undo your hard work up to this point. It may set you back if you throw everything out the window, but even that isn't a "do or die" scenario. Leave your perfectionism at home. Think of who you are seeing and why you are there.
The holidays are much more than pumpkin pie. It is also a time of giving thanks for so many things we all possess in our lives.