We are going to my mom's, so I don't have to cook at all!
Here are a couple sidedishes that have been on the Thanksgiving table before...warning: they are NOT healthy...one year, Mom made all of these (plus turkey, stuffing, gravy, mashed potatoes and green beans) and the lot of us practically rolled out the door.

The advantage is that all of these can be made tonight and then cooked tomorrow.
Butternut Squash: Boil a package of butternut squash until soft. Mash it up with 3 tbsp butter, tsp or more of cinnamon, 1/4 c of maple syrup or more. Cover and bake with other stuff in oven.
Cauliflower Casserole: Melt 2 tbsp butter in pan, add 2 tbsp flour. Cook until bubbly. Add 1 c milk, whisk to blend. Continue whisking until mixture thickens. Add 1 c shredded sharp cheddar cheese. Put 1 head's worth of cauliflower florets into buttered baking dish. Pour cheese mixture over it. Top with additional cheese. Cover and bake for 45 mins to an hour (depending on oven temp) until cauliflower is soft. Uncover and cook an additional 10 mins until cheese on top browns.
Sweet potato casserole: Cook several sweet potatoes (in oven or microwave to save time) Peel and put in blender bowl. Add 1/2 stick butter, a tbsp of brown sugar and a tsp or more of cinnamon. Beat until smooth, then add 1/4 c or more of heavy cream. Put mixture in a baking dish, top with walnuts and bake covered until hot and bubbly. Uncover to toast the walnuts.
Sorry this is so long. Have a great Thanksgiving!