I am also thinking of the age appropriate parts of what I do or did.
1st Christmas - so it's special.
DD was just a year then (Boxing Day baby). She loved getting a bit mucky making cookies for crèche. I basically made them and she got to shake the sieve, mix the eggs with a fork before they were added, put in a spoon of flour into the bowl, and then had a small rolling pin and her own cutter to make her own cookies (so I knew which ones to keep for home consumption!!). But standing up at the counter (maybe pulled alongside in highchair?), small apron rolled up to fit her, had her own wooden spoon to bang on worktop....They can be for home, family or nursery.
(In our case, she made that exact recipe with me for the next 4 years - a gingery spicy flavour, before going on to more plain sugar cookies that she now makes, complete with chocolate chips, all by herself).
Going for walks in early winter on dry days, we collected pine cones. Then on wet afternoons, we painted those, covered some in glitter, tied on ribbons, ....to make decorations for the tree.
Also, just colouring in and other kinds of decoration making are great. Free printable pictures from the net (Activity village or DLTK have loads of choice) and a handful of crayons. Or with paint. Fingerprint pictures using fingerprints to make shapes like decorations on a Christmas tree branches, birds (you fill in feature details), Santa faces, ... there are loads of ideas. Cut out shapes in cardboard, have cotton wool or card/paper shapes to glue on, and make tree or window decorations. DLTK was good for ideas, and loads of blogs etc are worth a goo. Toilet roll middles for Santas, snowmen or penguins, or getting creative to make reindeer etc too.
One evening when it has gone dark, and DC is in good form, bundle them into PJs with bottle/warm milk, and go for a drive (on pre selected route) to see the lights in your area. Whether that's street in town, or the various houses that are well decorated.
Singing Christmas songs and carols to him while you are doing things around the house. And play Christmas music on CD/Radio/ipod...., watch the Snowman!!
We got "Twas the night before Christmas" that 1st Christmas, and I read it on Christmas Eve every year. I also have loads of other Christmas books - from toddler flap and peek-a-boo ones to detailed stories etc. They are allowed out once it is December (except TTNBC - that's 24th!!), and while I don't do stories everynight anymore (down to twice a week), we do still read those a lot and DD now reads them herself.
We have always had a tradition of the Christmas candle, going back to our own childhoods and before. The youngest in the household always lights the candle that shows the way to the weary travelers, and that there is "Room at the Inn" for anyone who needs it. We don't put it in the window, although some still do. But even quite young babies can do it with the long matches or a spill (like they use in Churches for the big candles), and having a DMum or DDad hand very carefully guiding them! We also use that point of the day on Christmas Eve, as it gets dusk and we are having some quiet family time, to reflect on the year that's gone (good and bad), consider the year ahead, and also think of those no longer with us or who are not as lucky as us and consider our blessings. We usually follow that with a prayer (not a whole decade of the rosary like at home, as we are not particularly religious - but it is lovely just as a period of reflection without any prayer).
DS may not be interested in Christmas dinner exactly - depends how he is with the different foods by then. But try to have something that he likes, and give him at least some of the main meal. And while everyone else might tuck into pudding, cake, nice desserts etc - maybe have some jelly and icecream or a nice desert that is special and suitable for him too.
Definitely have a stocking. Don't be surprised if boxes are more fun than actual toys.
Get a Christmassy bath bomb or nice bubbles for a relaxing Christmas eve bath. We do new PJs for everyone (DH, DD and I) in our house, bath bombs for DD and I (a nice showergel for DH), and I put a naice hot choc for each of us in the Christmas Eve hamper too, and the book. (Naice means the block of milk choc to melt off a wooden spoon for DD, dark choc and chilli or choc and orange one for DH, and the sinful dark choc and squirt of amaretto for me!!).
DD loves stuffed toys of all sorts, always has. She has a moose that comes out at Christmas, and a Santa with his sack. And a smaller reindeer appeared last year from somewhere. (We also have a ghost at Halloween). They are nice to have and to appear again in decmber.
If you have a chance, try to do short shopping trips, I know DD hated shopping anyway and it's so mad and crowded in Dec that she used to really freak out. So a short stint and then off to a coffee shop for lunch or coffee, allowing her to get out and move around, was vital. And make time in the trips to see the lights, and decorations in shops, and the wandering Santas or whatever. Don't worry too much about having to "see" Santa this year, he's still very young for that and often the smaller ones are more scared than enjoy it.
He won't be able to help much with the preparations yet!! But, he might enjoy posting the cards in the postbox, and looking at the cards as they come in. If you need to keep him away from the current cards, maybe either get a few of last year's from the corner they got put into, or get a couple of blank ones, that he can look at the pretty pictures, scribble on, play with generally.
And definitely get at least one heirloom decoration, that you put safely high up, for his 1st Christmas. If you can afford something like a Royal Doulton, Waterford Crystal, ....really nice one with the year on it, that would be lovely. But there are loads ranging from really cheap and DIY, to really nice but still moderately priced ones (crafty ones - wooden, fabric, pottery..all sorts) that you can get personalized with the name and/or date. Or a "Baby's 1st Christmas" type too - but that may not be one they'll take with them leaving home 
.