What does a rationalist do for Christmas (or whatever analogue is going on around you at this time)? Stay at home and grumble, "Bah, humbug! Stop having-fun-for-bad-reasons, and did you know that Láadan has a single word for that concept?"?
Attempting to light a candle instead, I am giving my teenaged nephew, who was into science but is now into history, "Guns, Germs and Steel", which combines both. Someone else (I haven't decided who) is getting "The Atheist's Guide To Christmas" which has chapters by Richard Dawkins, Ben Goldacre, Simon Singh, and the like.
What are you doing for Christmas?
Echoing everyone else, I don't see why I need to give up my cultural traditions because they used to be associated with false beliefs about the world. Rituals don't have propositional content, so practicing them doesn't make me more wrong. We'll even have an angel on the top of the tree because angels are prettier to look at than stars (which have their origin as religious anyway). Also, I'll be listening to religious Christmas music because the traditional stuff is way better than most Christmas pop. We'll have a tree, lights, and probably some jokes about how Mary really got knocked up by a Roman soldier.
Pa rum pum pum pum!