I am rubbish at pastry to buy that usually - but make my own sausage stuffing for sausage rolls - taking GOOD sausages from local butcher and adding a few seasonings and fresh herbs from the garden.
I usually make giblet stock for the gravy, but I always use Bisto powder for the base of the gravy. (Regular roasts as well).
I buy mince pies from M&S. Sometimes I make mince meat, and occasionally remember to make the mince pie pastry I have a recipe for (it's quite a sweet pastry, the only 1 I can make, and works well for apple tarts too). But 9 years out of 10, we only have M&S ones here.
I tend to do the turkey dinner pretty much from scratch at home. DH does it with me. I certainly always do my own stuffing (well, I'll do it if I get a chance, but mine is plain bread stuffing whereas DH grew up with 1 including sausage meat so every Christmas Eve there is a traditional phone call to his DM to check how to cook the sausage meat for the stuffing before he puts it all together).
But I buy in DD's birthday cake (M&S on Christmas Eve for Boxing Day), and usually 4-5 packs (or a few more maybe) of nibbles from them as well for her birthday afternoon (we are basically "at home" to neighbours and family living near us all afternoon).
I will make a few other nibbly bits though, how poncy depends on my energy levels and expected number of guests (usually more guests = simpler nibbles).
And I make my own mulled wine. Lidl's is quite nice, and I usually have a few bottles of M&S non-alcoholic version for drivers, but my own is very simple to do but has a nice spice to it as well as fruitiness.
DM makes a pudding for us every year. DMIL used to make a cake but hasn't for a few years. But we get some when we visit both sets of DPs so don't miss out. I somehow cannot bring myself to buy either as I have been let down by not matching up to the HM versions in the past.
We make cookies for Santa - basic enough (non-Christmas) recipe. I sometimes bake other things, and sometimes make chocolates or sweets, could be alone or with DD. But that depends on how manic any particular year is.
We usually put together a gingerbread house. ONE year, DD made the walls (we had a particularly good au pair that year!). But mostly we buy the kits from IKEA (and once from Lakeland), and a bagful of cake decoration bits and other small sweets to add to the pile of decoration elements, and they work perfectly well for our needs.
We have an annual special treat of Ham and Stilton potato gratin for a leftovers dinner. So I always make stock from the turkey bones for this and freezing any leftovers.
I have recipes galore to try out, particularly for sweet treats. But never find the time for that.