Christmas tree no doubt..
Also, regular pinetrees for the arctic biome if that isn't in yet.
And I think there would be a new crafting system like alchemy, runecrafting or more advanced cooking added, a couple of Christmas specific recipes like gingerbread, present boxes to put items in.
Oh and furniture if that hasn't been added by then.
Basically all you need to have a nice Minecraft Christmas.
Oh wait! And smoke blocks, otherwise there won't be any chimneys! ;D
Smoke is a brilliant idea no matter which update you stick it in. Could help you spot civilization from great distances!