It's a feast day for me (i.e., off plan) but since I'm vegan anyway it's not MUCH off plan. My stepbro and his family are all vegan and my stepmom and father mostly go along, so there's TONS of vegan options available. I usually bring a Tofurkey b/c I love them. Of course they are NOT McDougall legal, but if anything qualifies as a feast day, T-giving does, right?
I find that most meat eaters like Tofurkey. Make plenty of stuffing (no oil--easy to keep pretty McDougally) and gravy (in addition to what comes w/ the Tofurkey, Hain makes a nice dry gravy mix that is good. Then just serve lots of veggie dishes and try to keep those McDougall-legal. That way you won't get TOO far off.
If they want to make a few non-McDougall items (i.e., meat/dairy esp), let them--you don't have to eat any of that stuff.
Here's how I look at it: If the celebration is at MY HOUSE, it's done MY WAY. If I let you make something you want to eat and I don't you should be grateful. Otherwise, just shut up and eat.