Feel like I gotta add the Australian perspective.
To quote Tim Minchin, Christmas is all about white wine in the sun. My family usually nips down to the beach for an early swim at about 0700. The roads are empty and there's nearly always a beach-related gift under the tree.
Lotsa seafood. Prawns are a must. I usually queue at a local wholesale fishmonger at about 5AM on Christmas Eve to buy a coupla kilos of prawns. There's then a nice moment when the best prawn-peelers in the family don aprons and get 'em ready to cook.
The prawns kick things off and there's usually a big roast something too. If possible we get it done on the BBQ with the lid down, to keep the heat outside rather than cooking the kitchen.
By mid afternoon it's best to keep drinking - stop and the heat means you get a 4PM hangover