Very little.
At least one half batch of cookie dough, to slice and bake from frozen (in case we don't have either the time or the energy to bake cookies from scratch on Christmas Eve for Santa's snack). I just make a large batch sometime in autumn and freeze part of that in greaseproof paper.
Sometimes, some pastry or already assembled mince pies. (The years I am truly organized).
Chicken stock from a roast at some point, or better still, turkey stock from Thanksgiving dinner in November, for making the gravy. (TG is a small turkey joint that I cook after work on TG day - no great effort is made).
And breadcrumbs - I make those with any odd heels and crusts and leftovers over the course of the autumn, especially if we get any particularly nice loaves! (And then I end up using loads for stuffings, covering chicken goujons or crab cakes, sprinkling over the mashed potato top of smoked fish pies etc).
I know lots of people talk about roasted potatoes already parboiled and fluffed, or roasted roots done the same, or red cabbage etc. But we don't eat red cabbage, and I like to do the veg fresh on the day. We're not catering to loads - we peel and chop everything on 24th (or 23rd if we will be extra busy), and just leave most things soaking in cold water (potatoes, carrots, etc) with a few in airtight containers and no water (parsnips, onions, garlic), and DH makes the stuffing on 24th as well. So it's easy then to cook them quickly on 25th.
Oh - I DO make sure I have lots of ice cubes made.
And I also generally have sliced lemons and limes there too for drinks - we only ever use a couple of slices and got fed up wasting so much, so slice the whole fruit and freeze the spares and they work really well in drinks straight from freezer! I usually try to add a few extra before Christmas when we might expect visitors.