What do you prepare ahead and freeze?

Stuffing definitely.  As for the pie, I'd probably do it the day before at the earliest.  Yes you can freeze it but to reheat it takes as long as baking.

Some of my prep I do ahead and freeze. Turkey stock and chopped meat for the stuffing is done and in the freezer. Dinner rolls are made and into pans and in the freezer to be thawed and baked when needed.

We usually do most of it the day of as we usually don't eat until 2pm or so.  The few things I do ahead are make turkey stock a few weeks ahead and freeze-no way to get enough stock for everything from 1 turkey, plus need plenty of stock for stuffing and it wouldn't be ready in time.  I usually make the pies a few days ahead.  As for dinner rolls I will often mix up the dough the night before and let it do a slow proof in the fridge.  Also tear up the bread, for stuffing, 2 days in advance so that it has time to dry out.  Other than that its all done the day of, but my family all cooks and we often gather in the kitchen so there is always plenty of people to be put to work.

I don't host Thanksgiving but I do host lots of other dinner parties throughout the year and I always like to prepare in advance.  With a little good planning it is possible to make things as fresh as possible and utilizing the freezer can be very helpful.  Like the others stated I make chicken stock weeks in advance when I know I will need gravy.  I do a lot of cooking the day before as well and one thing that has always helped me is preparing all my mise en place the day ahead, as well as preparing all salads and dressings too.

I'm bringing the bird, stuffing. gravy and  green salad. Everything prepared day of, except for the corn bread for stuffing.

I'm visiting the parents this week, and we are eating at their friends house.

They have been quizing me every day about the logistics, wondering why I have not started doing all my chopping and stuff. They think dinner for 10 is a week long project, not a few hrs.