I buy plenty of part baked french stick batons (half size of a french stick) and ciabattas so that I can bake extra bread as needed in minutes. I always buy some naice sourdough kinda bread for Christmas Eve (we do a nice buffet of cold meats, pate, cheese, salad bits etc Christmas Eve so it gets well used then).
I have enough cheese, pate, olives, pickles, chutney, salady bits etc to nibble on for the next few days. The Christmas Ham and Spiced Beef are great for sambos too. And a full dozen eggs or more for various uses (scrambled, fried, boiled, poached, baking, crab cakes, ...).
Bags of nice crisps and nuts, amaretti biscuits and regular biscuits for nibbles. Mince pies, or frozen pastry and jars of mince meat (I happily use pre-rolled at this time of year, but it's HM mince).
I try to have a lasagne in the freezer in case we get visitors 1 evening. I like to have sausage rolls roo (I try to make my own, but don't always manage it) or at least cocktail sausies.
Plenty of soft drinks (we generally use cans all year as bottles go flat before we finish them, but I do get bottles for Christmas), and tonic. I'd always have tea and coffee for the plunger anyway, but I need to remember cream for Irish coffees.
I always have a couple of the tins of croissants you roll and bake yourself, for breakfasts. And a bag of brioche type pastries too. Oranges and grapefruits for juicing for breakfasts (and lemons and limes for drinks and a cheesecake if enough visitors are likely).
And the freezer also has things that I normally have but am doubly sure to keep at Christmas - cooked prawns (to serve cold or throw into a sauce with rice or pasta), crab meat (to make crab cakes from leftover mash, tin sweetcorn and leftover bread crumbed), frozen peas, and some decent chicken nuggets and oven chips.