We travel to four different places over the Christmas week which is a nightmare. I'd say my biggest tip is to not take toys, lots of times in the past I've thought I'd take lots to keep DC entertained which is always unnecessary suitcase space. Now I just take pens and loads of paper! Much more space economical.
And also to just fit in with however the people you stay with do anything. I spend my whole Christmas biting my tongue, sleeping in freezing cold beds, kids eating terribly etc because so much easier than speaking up: