I'll be skipping the overeating, but not the holiday.
I totally get where you're coming from, gabrm. I have that fear of falling into a downward spiral around the holidays too. My approach to it is going to be to treat it like every other day, and by that I mean I will make a plan, track my calories, stop eating before I physically hurt, and get some exercise in.
That approach has worked for Fourth of July, Labor Day, Easter, birthdays, and vacations. It should work for Thanksgiving and Christmas too.
Luckily for me, I make dinner in my house, so I'm completely in control. If I wasn't, I think my plan would be to take a serving of meat about the size of the palm of my hand, starches about the size of half a tennis ball, a large serving of any veggie that looks like it's not swimming in cream, skip the bread, and have a slice of pie about the width of my thumb.
My point in the " how I'd eyeball portions at Aunt Fanny's Thanksgiving Throwdown " paragraph is just to say even if you can't calculate the calories exactly, you can still exercise some portion control. And you can stop if you start to feel full.
I can also understand, and I have been that dieter that says " Hey, it's once a year, I'm gonna get my gravy on! " Nothing wrong with that. I just don't do it because my digestive tract, after years of bingeing and gall bladder surgery, is REALLY fed up with me stuffing myself like I was the Thanksgiving turkey. Acid reflux and gastric dumping ( google that ) just aren't worth it. Neither is being crazy hungry for the days afterward until my body gets used to 1500 calories a day again.
Whatever you decide to do, I hope you enjoy all yourself this Thanksgiving.

And let us not forget, there's gambling on football and binge shopping on Black Friday if you need a replacement vice. Just kidding.
