For me, the key ingredients are a roast bird, ideally turkey but a good chicken or duck would do. Really good roast potatoes, parsnips and carrots, pigs in blankets, home made stuffing, good gravy made with wine and fresh herbs, baked red cabbage and sprouts (which I like with pancetta and chestnuts but DH prefers steamed so we go for the easier healthier option. Cranberry sauce is good but not essential.
No cauliflower cheese, no yorkshires, no broccoli. I do peas for DC as they don't like sprouts.
Pudding is traditional Christmas pudding lit up with warmed brandy and served with custard or cream.
Candles, crackers to pull, paper hats, stupid jokes, lots of wine.
Good chocolates and brandy or whisky. (We eat it in the evening, not lunchtime)
That's it.
I like it really traditional. But am very happy to have salmon and caviar blinis to start or a cheeseboard afterwards etc if people who are hosting insist.