I also start buying super-early in the January and summer sales. I get things like partywear for gifts for the following Christmas often less than half price, then add a few discounted books from The Book People and a few small sale toys and bingo! done for nieces and nephews for the following year! The same goes for toiletries for elderly relatives, etc. - I hit the Boots sale in January when it goes down to 75 percent off and stock up on gift sets for a fraction of the pre-Christmas price. You need some space to store bargains, but if you do you can make fantastic savings.
I also have a big stash of cards and wrap in the loft, all bought when they were massively discounted (eg. in the end of the Christmas sales some years shops like John Lewis discount their wrap to about 50p a roll and it's great quality). I must have enough at the moment to last several Christmasses! I plan to wait until I've used them all up, then do another sale buying frenzy. Oh and I also make sure that when I pack it all up for the following year, I toss in some cheap rolls of sellotape and a pair of scissors so there's certain to be some to hand. I also stock up on nice decorations in the sales, too - and if I find I have bought too many, I redirect them as small gifts to add to presents the following year.
I aim to get all my presents wrapped up really early in the autumn and, if possible, dispatched up to far-flung relatives a month or so in advance. I like to have them all off my hands by the start of December (for the people I won't see in person during the festive season). I also write my cards early - I like to have them all done and posted by 1 December. Then I can enjoy the month doing nice Christmassy things with my small DD and soaking up the atmosphere!
I actually do it so early because it really stresses me out to still have presents to get and wrap as Christmas approaches, so it's less being highly organised and more self-preservation.
Food-wise we normally go to relatives but this year we are staying at home. On Christmas Eve we will go to the local Christingle service, so some hearty pea and ham soup and bread sounds like a nice supper afterwards, followed by DD putting out a mini mince pie and glass of port for Santa! On the day itself I am thinking of either booking a pub or ordering in ready-made stuff - but in that case not doing a traditional turkey but maybe something like roast beef or steak. We don't drink much, and want not to stress out about cooking, so I'm planning frozen bake yourself pains au chocolat for breakfast; and then a half-bottle of champagne plus smoked salmon and soda bread for a starter whilst opening presents. Then the main course - perhaps beef medallions, frozen roast potatoes, and ready made roast cabbage, pigs in blankets and roast carrots in a tray? (I'm not fussed about stuffing or sprouts so can happily leave these this year.) For pudding, I intend to buy a small microwavable pudding and some cream, and a trifle or raspberry jelly for those of us who don't like Christmas pud much. A couple of cheeses, and a ham and some salad for the evening, and we're all set! I'm also going to stock up on pasta, parmesan and fresh ready-made bolognese and tomato pasta sauce for quick meals between Christmas and New Year. I save up points towards a slightly bigger than normal supermarket shop at Christmas so we don't have to be popping out all the time. I try not to go overboard with the Christmassy food and eat as normally as possible for most of the time - otherwise I put on loads of weight over the holiday and feel rubbish in January!
December for me is all about the experiences - seeing the Christmas lights on in town, taking DD out to a carol service or for hot choc. Our local National Trust house does some nice Christmas events, and there's a couple of children's things on at work that I might take DD to. I may even book a panto this year for the first time - I think DD might now be old enough to enjoy it (though I hate the panto...it takes me back to childhood Christmasses though!!)