There is a lot you can do ahead of time to make it easier, and also some thinking which will also make it easier on the day.
I am not great on prepping really early and freezing – although lots of others on here are great for that – more of doing a few things in the days before, prepping veg etc on Christmas Eve, and taking a relaxed attitude on Christmas Day itself.
Anytime from now on that you have spare time, you could make breadcrumbs (and indeed, the stuffing), chicken/turkey stock (or the whole gravy), and blanched green beans (I tend to do those from the garden in summer) to freeze for Christmas. (And some mince pies if you like homemade versions).
My DM does cauliflower cheese ahead of time a lot – but the whole cauli as a single piece. I do freeze leftovers if I have any, to have as a sneaky dinner myself some nights (just cauli cheese and roast spuds is yummmm!) – but I always do mine as florets. So making it for Christmas dinner would be fine. (I know that’s not on your list but that’s one I know).
For veg prep, carrots and spuds and brussels sprouts could all be prepared on 23rd or 24th, and left soaking in water (in a pot or plastic containers). If you do them on 23rd though, change the water on 24th. I tend to peel and chop them literally ready to cook – but I know others par boil the potatoes and toss them in goose fat at that stage to put them on a roasting tray in the fridge (and some even a few weeks ahead, and freeze on a flat tray of some sort, before bagging up when frozen, until defrosting on a roasting tray ready to put in the oven).
Parsnips I would only peel and chop on Christmas Eve, as they go slimey if left in water but I don’t want them to dry out much so I leave them in a sealed plastic container. Cabbage would probably be similar, although that could be left in water, but I would only do it on 24th.
I also peel and slice onions, again in sealed plastic containers, some of which DH takes for the stuffing (sausage meat and breadcrumbs based) that is made on 24th, and the rest for roasted veg the next day. And a few cloves of garlic get peeled into a separate small tub.
I make a flavoured butter in the week before Christmas (some evening it’s relatively peaceful). Lots of herbs (definitely sage and thyme, maybe some rosemary and/or parlsey as well), salt and pepper, and some crushed garlic. I leave the butter soften all day in the kitchen, mix it in the evening, and then roll into a log in some greaseproof paper, which I let harden up in the fridge until I need it. Then I can slice it neatly or take out a big dollop to soften up (for pushing under the turkey’s skin). This freezes well also – which can be nice if you have lovely herbs in the garden in the summer.
Also on 24th, I will try to organise any herbs I need which are not in butter. So my roasted root veg involves some balsamic vinegar, olive oil, juice of a clementine, salt and pepper, crushed garlic, oregano and thyme (maybe rosemary?). Officially (it’s a Jamie Oliver recipe) you put the parboiled/steamed carrots into the clementine and (1 of the herbs) first, and then toss those with the parboiled/steamed parsnips and onion into the other seasonings – I just put them all into the whole lot together. But it can be nice if the flavours mix beforehand (and you have less messy stuff to do) by putting all those seasonings into an old plastic cream bottle (200ml or so) or a small plastic tub on 24th. And I may do another small plastic tub of chopped herbs for scattering over various things – any that I don’t use on Christmas Day will probably get used in making turkey stock or I can freeze to use another time.
Regular bisto gravy, with any juices from the meat (and a good slug of wine if your family would like that), would be relatively simple to make on the day (I sometimes mix the bisto powder with a good glug of red wine and any stock from freezer on 24th, so I am just pouring into the roasting tin on 25th – it’s only a small saving of time/effort but sometimes seems helpful). Or you could make the gravy in advance, slightly thicker than you'd like, store in fridge/freezer and add juices when reheating.
Lots of soup is good for freezing. Or prawns. You could make up the marie rose sauce on 24th, and leave that in a sealed container in the fridge (mine is: mayonnaise, ketchup, a couple of drops of tabasco and a small squeeze of lime juice). You could also have the presentation bits somewhat sorted – iceberg washed and chopped in a plastic tub/ziploc bag, cherry tomatoes washed or full sized tomatoes washed and quartered in another sealed tub/bag, and a jar of capers sitting somewhere near those ready to just drain (if you like those). But I would leave the quartering of the lemon until 25th so it doesn’t dry out at all (separate to sliced lemon for drinks – see tip below).
The sliced lemons is a trick I learned a while back - we only ever tend to use 2 slices at a time, so wasted loads. Now I slice a whole lemon at a time, and freeze any spare slices flat on a tray, bag them up once frozen, and when needed, throw them straight from the freezer into drinks where they are perfect - and saves an icecube as well! It also works perfectly for limes.
If you are cooking a whole turkey, there is plenty of time once that is out for the rest of the meal to finish. So get the turkey in the oven early, and relax for a while.
About 30 minutes before it’s due out of the oven, boil some water and then par boil the potatoes. Get out the tray they will cook on, and put the goose fat (if you are using that) onto it, then put the tray into the oven about 5-10 minutes before the turkey comes out (heats up the tray and melts the goosefat). Drain the potatoes, toss the goosefat into the pot (less mess that way) and give a good shake before emptying the pot onto the hot tray.
Take out the turkey, put in the potatoes in the oven and turn up the heat.
Put the turkey on a carving plate, cover with a double layer of tinfoil, and lay a bath towel (doubled over itself) over the top. Let it rest for an hour (it will stay hot for 2 hours this way!).
The potatoes will probably need a little longer than the roasted veggies, so I tend to only start to parboil those once the turkey is out and spuds in. Pre-heating their tray also helps, but is less vital.
While they parboil, might be a good time to strain the fat off the turkey roasting juices, and make the gravy. I tend to make it in the roasting tin to get all the flavour left in the tin, but then put it into a pot to allow reheating as we serve. Add back in any meat juices (you may want a small separate pot of gravy/a sauce with no meat juices for the vegetarian).
Once the veggies have parboiled and are going into the oven, it is probably a good time to turn on a low heat under the other veg in pots on stove, and on gravy if reheating it. Soup may need to be turned on for reheating slightly earlier, or at a higher temp. And if there is a “main item” for the vegetarian, allow for that in the oven as well if necessary.
Basically, think through the menu, and how long each item needs to cook. Work back from the time you serve at (bearing in mind that some things can slowly cook or reheat for main course while you eat starters), to get the time they need to start cooking at. Then write down a list of those timings. (I find that using a timer can help for certain things – but I don’t worry about most).
But also, give yourself an allowance to let things run late. Have some extra nibbles, in case you need some more time to cook/serve. As long as the meat is thoroughly cooked, it’s fine if veggies are a little crunchy, or a little mushy. Give people jobs to help, if they won’t get in your way or cause a flap – or tell them to stay out of the kitchen if you need them to (they can always do the washup later).
The day before is fine, but plan your tools and utensils as well as the menu. So if you need certain knives or spoons clean, make sure they aren’t sitting in a dishwasher waiting to run after Christmas morning breakfast (just when you will want them!). You probably will already have made sure that you have the right pots/trays etc, and that you hadn’t planned on using 1 tray twice at the same time (using it once and having time to wash and reuse it is fine if necessary – just not at the same time).
And if you have spare space (heated tray, hostess trolley, second oven) to keep food warm is great. Otherwise, heat the serving dishes (even just letting hot water sit in them for a few minutes and drying off again works well) before putting the food into them.
Have a basin full of hot sudsy water once you start having tools/pots being finished with. You can just dump them in the water to soak, and wash a few bits as you go along and it makes a huge difference to having space on the counters/cooker to work with.
And make sure someone is in charge of keeping the chef’s glass of mulled wine topped up, and having a chair available for when the chef can leave the kitchen for a while and sit with everyone else.
Sorry, I just realized this is epic 