Thanksgiving marks the start of the "danger time" for people with food allergies. Its always tough - we all have horror stories about being inadvertently exposed.
We would love to eat your food, truly, but we are scared to death of having to spend the rest of the holiday weekend in not-so pleasant ways. I'm not saying this to put a damper on your Thanksgiving, but to illustrate that it can be as simple as using butter (or margarine) that has crumbs from toast in it to glutenize someone.
It sounds simple; no wheat, rye or barley. But there's breadcrumbs, soy sauce, condensed soups, pie crusts...basically the only time something could be safe for me would be the mashed potatoes and cranberry sauce.
Even the turkey, if you've stuffed it, is off-limits (I've stuffed turkeys - I know that stuff gets everywhere!). If someone takes the crackers out first, then the cheese, the cheese can have crumbs on it. (I have been glutened by cheese...)
What to do? I don't want to show up with my own meal, that's ungracious. And of course I can bring a dish (and usually do). And I hate sitting there feeling like I'm sorry, I can't have that, or playing 20 questions. But I do love the company, and that is the main reason I'm there. So if I'm not eating your food, its because I'm scared.
So what can you do, if you know someone can't eat gluten? Keep the crackers and the cheese on two different dishes. Or offer an appetizer they can eat...sometimes I'll use little potatoes cut in half and roasted, topped with a little creme fraiche and smoked salmon. Devilled eggs work too (just make sure the mayo is out of a fresh jar or a squeeze tube).
Prepare the gluten-free offerings first. Make the turkey without stuffing...for dessert, maybe make a pumpkin cheesecake without the crust (or else use gluten-free gingersnaps).
Then, on the day, let the gluten-free person serve themselves first. And let them know which dishes are gluten-free.
There are some decent gluten-free breads, I like Udis. Some people swear by Schar. And some decent gluten-free crackers; Namaste mixes are good. Just remember to keep anything gluten/gluten-free in far corners...if you have any questions about adapting recipes, just ask. Remember to read all labels, gluten can hide very easily.