Best way to keep food warm for a summer BBQ?

I'm having a BBQ tomorrow for son's birthday. I'm looking for ways to best prepare the side dishes. I've done a bit of online research and some advice to make an hour before guests arrive and other advice says to make the night before and reheat. I'm looking to make boxed mashed potatoes but am wondering what people mean when they say to add cream and er to the already made potatoes? I'm going to make them tonight, refrigerate and crock pot them tomorrow on warm to reheat. If someone could tell me what type of cream to add, I'm just confused on that! Any other advice would be appreciated! THANKS