If you are planning now, even everyday things like lasagna can be slow cooked with loads of veg and half a bottle of wine reduced down into for the sauce type luxury versions.
If freezing mash, make it with dried milk powder rather than liquid milk. As it absorbs water in the freezing/thawing process so the dried version is perfect rather than sloppy.
Obe suggestion might be a few days doing a good curry now but big pot of each to freeze half - in individual portions. So you have capacity for individual meals or adding one extra easily - but also o have a few different types available to do more of a curry feast over Christmas with little effort. Defrost enough servings of 2/3 types for your quantities eating, serve in the middle of the table for sharing with an easy pulao rice and some chutneys, puppodums (from shops) and diced tomato/red onion/black pepper mix. (I do a pulao that involves frying 3 cardomon pods, 5 whole cloves, about 10 whole black peppercorns in some ghee for a minute, add the basmati that’s been rinsed 3 times for a minutes, add your boiling water, salt and good pinch of saffron and leave to cook - 1 cup rice to 2.5 cups water).
Lovely unctuous stews are already covered.
My other oven bakes include shepherds pie, chicken and mushrooms in a cream and wine sauce (under mash or pastry); poached smoked haddock flaked with brocolli florets in a white sauce made using the poaching milk under mash and topped with breadcrumbs and some grated cheese.
I also like to put things like chicken joints in lemon and garlic Greek marinade; chicken breasts in piri piri marinade; lamb chops with garlic and rosemary marinade etc into bags ready to cook. And diced Mediterranean veg freezes well to cook from frozen - doesn’t matter what size (I do big in bbqs in summer, fine dice for dinner parties..) but that the veg are all the same size in the batch. Onions (red are nicest), whole garlic cloves, red and yellow peppers, mushrooms, courgette, (aubergine if you like it), mange tout/sugar snap peas, french beans - whatever you have and like. Toss with seasoning - some olive oil, dash of balsamic vinegar, herbs like thyme, chopped rosemary, oregano, salt and pepper. Bag and freeze. Cooked leftovers also freeze well to reheat as a side dish, chuck into tomatoes for ratatouille or plain tomato sauce/with added meat for a pasta dish.
I also like to have a few rolls of different cookie doughs to slice and bake, as some previous posters. I always plan mince pies but usually get as far as the pastry but not even making the shells before freezing (I use the Hairy bikers pastry with grated orange zest in it). I’ve also frozen Jamie Oliver’s sweet pastry (from original Naked chef book) as a lump or blind baked for easy tarts. Or a bag of crumble mix so I can grab a bag of frozen berries, rhubarb from summer freezing or someone has volunteered to peel apples into a baking dish and add some crumble on top to throw into the oven, especially if it’s already hot for main/sides.