I go to meals out and family dinners and either don't eat, or, more often, eat only what I'm ok with - even if that's just soup, bread, or whatever. My family understand this. How much do your friends know about your disease? I see no point in making myself ill just to conform to social expectations. It can be awkward with new friends or people I don't know well - I do tend to avoid eating in these situations - but if it's a meal with someone I'm close to then what I eat isn't an issue. If you're celebrating Thanksgiving with them, perhaps you know them well enough to share more about your disease?
For Christmas dinner with my family (no Thanksgiving here) I'll probably have some turkey and potatoes with gravy. I've got a new ileostomy so I'm not quite sure yet whether I'll be able to handle other vegetables. My portion will be tiny compared to everyone else's.