My family were very unchristmassy - mum being v. religious, contemptuous of consumerism and a non-drinker to boot, the tree went up on Christmas eve and came down again asap, we had small presents, a chicken dinner and the day was all about God. I'm making her sound like a right mingebag, she wasn't really, she went to town for our birthdays, but Christmas was to celebrate God's birth, not ours.
As for my OH's family... well, they're a lot more secular (and rather more fun!) but the only actual tradition that springs to mind is if someone offers wine at the dinner table, the automatic response has to be everyone flinging their heads back and going "Ahwhoooo!" .... first time it happened to me I was a bit 'what have I married into??' but now I howl along with the rest of them...