I am going to mostly stay on plan, but this is the ONE time during the year for bread stuffing and I'm going to have a small serving as a planned indulgence. I'm not a big Thanksgiving person. I don't like turkey, I can live without mashed potatoes, marshmallow sweet potatoes, pumpkin or pecan pie, etc, but I love stuffing (and not a low carb substitute!)
Here's how I handle my planned indulgences:
I eat well during the day leading up to the indulgence meal--no fasting or eating less in anticipation. The idea is to eat a little just for pleasure and not be super hungry so I'm tempted to binge.
I will eat a hearty and mostly low carb meal. That means I need to eat some turkey (meh), I will eat the veggies with plenty of fat, and I make some sugar free cranberry sauce just for me (regular for the rest of the family). We often make chopped chicken liver as an appetizer while the turkey is cooking, and I can eat all I want of that. Then I will have a reasonable serving of stuffing and enjoy the heck out of it. I will also make a flourless chocolate cake with erithrytol sweetener so I can enjoy a treat and my kids will eat that too, along with their pumpkin pie. And that's it. Indulgence over. No guilt.
I MAY have consequences--when I eat wheat I get pettichiae (bleeding under the skin) on my forearms (long story). I may get a GI response from the Metformin. I don't anticipate a huge spike in my BG, as I will be eating all that other fat and protein, but we'll see. I may temporarily gain a pound or two. But this is once a year, then I get on with my life, no big deal. This will be my 4th year on LCHF during Thanksgiving, and I've survived them all without losing LCHF momentum.
We don't celebrate Christmas, so I don't need to worry about that day or the holiday indulgences as they won't be around me. I will probably eat a potato latke or two during Hanukkah, but we generally make them ahead, freeze them and reheat them so they may have an element of resistant starch (I like mine with the sugar free cranberry sauce I make on Thanksgiving instead of apple sauce and this year I'll use coconut yogurt instead of sour cream). And I make zucchini latkes for myself, too. I can totally live without a jelly doughnut.
Personally, I think that if I didn't allow myself the very occasional and careful "indulgence" I'd have a lot harder time sticking to LCHF in the long term. I tend to rebel against strictness. Because I know I can have a little flexibility, it stays doable for me.