Some of these already mentioned, but I’ll repeat as a sort of ‘vote’
Prep and freeze as much as possible ahead. For me, this includes cranberry sauce; bread sauce; stuffing; red cabbage; carrot and swede mashed together, Delia’s Parmesan parsnips, sausages from our butcher wrapped in bacon before freezing. I have also started blanching and freezing sprouts end November/early December when they are at their plumpest. They get gradually smaller towards Christmas, I guess they are harvested increasingly early to meet demand. They can be cooked from frozen. If we are having cauliflower cheese (not routinely as I think there is enough going on but have a family member who wouldn’t forgive me if I didn’t make it, so we have it if they are coming), I make it the day before as I don’t feel it tastes as good from frozen (I know many people don’t agree, just my view).
Gravy: I am personally happy with Bisto with the turkey juices added, especially for big numbers. But if you want homemade, consider Jamie Oliver’s make ahead gravy using chicken wings. I have made it once, didn’t add all the spices he suggests but it’s a good base recipe. Or if you want ‘proper’ gravy, I’d buy it!
We have an electric steamer which is really helpful when cooking for big numbers, I also have a traditional steamer with two steamer pans from way back before electric ones were available. I use one for steaming the pudding (which I will make soon).
A tip I picked up off MN years ago was that the turkey can rest comfortably for a couple of hours, cover with foil and a couple of towels.
Re crockery: I prefer to eat off white plates. I have a set of plates I keep for entertaining/Christmas. Table cloth/runner/napkins/candles etc provide the colour theme rather than the plates.
B&M crackers are usually decent quality, with non-tat content. I’ve seen crackers with very similar content in M&S & John Lewis for triple the price. Regardless where you get them from, if you go for gold, you could buy ribbon in your theme and wrap around the ‘nipped’ ends
Christmas Evening we always just have cheese, patenand crackers. And our butcher’s lovely pork pies. Easy to assemble and enjoyed by most people. And lots of chocolates, Christmas cake and pork pie.
Having said I prefer eating off white plates, for the above I would be happy to eat off festive paper plates.
Christmas Dinner creates a lot of washing up. It’s the one time I would use disposable foil trays for potatoes and veg etc (although I prefer a more solid tray for the turkey)
Possibly not an issue if you’re only entertaining for the day, but double check you’ve enough kitchen roll, toilet roll, spare hand towels for the bathroom, tea, coffee, milk etc