I have a great recipe for Make-Ahead mashed potatoes, that reheat nicely in a crock pot.
HOLIDAY MASHED POTATOES
5 pounds Yukon gold or russet potatoes, peeled and cut into 2-inch chunks
1/2 cup milk
1 package (8 oz) cream cheese, at room temperature
1/4 cup (1/2 stick) butter or margarine
1 teaspoon garlic salt
1/4 ground black pepper (We add a very tiny bit of pepper, I do not care for pepper too much)
4 strips cooked bacon, chopped (optional)
Place potatoes in large saucepan; add enough water to cover. Bring to boil over high heat. Reduce heat to low; cover and simmer 20 minutes, or until potatoes are tender. Drain. Return to saucepan.
Add milk, cream cheese, and butter to potatoes. Mash with hand masher or electric mixer on medium speed until creamy. Stir in garlic salt and pepper. Spoon into a 12 x 9 inch casserole dish. Cover and refrigerate up to 24 hours.
Remove potatoes from refrigerator 3 1/4 hours before serving time. Coat slow cooker insert with vegetable oil spray. Place potatoes in slow cooker. Cover and heat on low setting 3 hours, stirring tiwce. Add chopped bacon before serving, if desired. Potatoes can be held ad additional 30 minutes if needed. Makes sixteen 1/2 cup servings.
NOTE: Mashed potatoes also may be reheated in oven. Bake uncovered in casserole dish for 45 minutes until hot. (SORRY - recipe did not specify the temp here.)
Sorry - I can't help with any sweet potatoes recipes - I don't care for sweet potatoes, so If I am hosting - I will always mentioned to my family that if anyone wants some - they ought to bring some

And - that is going to lead me into my next suggestion - if someone asks what they can bring - let them bring something! (When I do this - I know one of my sisters will always, always, always be late - so I suggest a dessert for her, my parents come from a distance - so wine is a good option for them etc.