I've been thinking a bit about this - at the moment, our Christmases are usually alternated between my family (small-ish) and DH's family (bigger, lots of children), and alternated round different people's houses - either at ours, or my parents', or any one of DH's family's houses all round the country.
This means it's quite different every year, and we have to do a lot of fitting round other people's plans and traditions - one lot love walks, the other side likes relaxing, one group love the Queen's speech, the others skip it but do church and carols, etc etc...
I would love to find some little things we can do for our DCs that would be personal to us, and can be the same every year - so they can get excited about those things and know what to look forward to a bit more - instead of it being all a bit random and different every time. (My background of every Christmas being fairly similar - and fairly quiet-but-cosy - is probably a factor here!).
So - do you have any little "things" you do which don't depend on where you are, what other people around are doing, etc? All the better if they are quite easy to fit in, so they won't get missed if we suddenly get steamrollered into "everyone has decided we are going to do XYZ now" 