Turkey- I found a crown is much easier/less faff. Unless you want loads of turkey leftovers then this is what I’d choose. I liked the Ocado ‘Black Farmer’ one. It comes with stuffing so that’s another thing you won’t need to do separately (it is expensive but most supermarkets have something similar).
Roast potatoes- These are the one thing I’ve never been able to prep in advance and still have them taste good. I’d probably focus on doing these on the day unless other people have tips.
Pigs in blankets/stuffing balls- Most supermarkets and butchers have them premade. They’re usually pretty good and it’s a good place to save prep time (there’s a negligible difference between store bought and homemade, especially with pigs in blankets).
Gravy- Homemade gravy is the thing I find requires most time on the day. Definitely make in advance and freeze or buy premade gravy (Tesco and M&S both do fresh turkey gravy at Christmas).
Carrots and Parsnips- Lightly steam or parboil the day before. Put them into the roasting tin. Just before roasting drizzle with honey, oil, butter, salt/pepper and thyme.
Sprouts- I prep them fully the day (including peeling, cutting in half and parboiling). Then on the day I finish them off by roasting them with pancetta, butter and chestnuts until they’re hot and the pancetta is crispy.
If you like them just steamed/boiled then I’d peel the day before and then steam just before eating (they’ll go soggy if you cook them the day before and then try to reheat).
Red cabbage- If only you like it but you want it then I’d buy the M&S premade one and microwave it.
Cauliflower cheese- If you want to make it in advance then I’d recommend parboiling the cauliflower slightly less than you would normally and then roasting it to make sure there’s no moisture which will make it go soggy in the freezer (you don’t want too much colour but it does add extra flavour too). Mix with the sauce and freeze. Don’t add anything to the top before freezing or cooking because you’ll probably need to stir it multiple times (I find that if it’s been frozen the sauce can end up watery/separated- after stirring it’s fine). Add any extra cheese and breadcrumbs about 10 minutes before the end.
If you don’t want to bother then Cook and M&S ones are nice.
Yorkshire puddings- Freeze brilliantly once fully cooked and can be reheated from frozen without any problems.
Any additional veg or sauces just buy premade (or cut them entirely). If your family love bread sauce then it can easily be made in advance.
Pudding- honestly I’d buy something premade but if you want to make it in advance the sticky toffee or chocolate pudding freezes well or a premade meringue is pretty simple (you just need to whip the cream on the day and add some berries).
Both M&S and Tesco do lovely fresh custard (the ‘finest’ one is just cream, milk, eggs, sugar and vanilla and basically the same as you’d make at home home but without the fuss). Or cream/ice-cream.