How to keep food hot in buffet for 40, & deal with those who dislike room temp food?
It's Thanksgiving. Everyone's food is room temperature. (Or, not to be nasty, show them where the microwave is!)
Crockpots, hotplates and double boilers if you have stove access. Some Thanksgiving dishes are better at room temperature! I'd let the room temp food haters get through the buffet immediately if possible :) Happy Thanksgiving!
Focus on keeping the gravy hot for the turkey, potatoes and stuffing. a crockpot is handy but that will only keep one item warm. You can warm the platters and serving bowls in the oven, I find this helps to keep the food warmer longer. Cold bowls will draw the heat from the food. As far as other items, I agree with Mark. Don't sweat it!
If they didn't cook, they can't complain. I put the mashed potatoes in a crock pot on warm which frees up stove space. I roast lots of veggies and serve them at room temp.