Make sure you have things you need like loo roll, kitchen roll (even if you don't normally use it, it's very useful for spills etc at Christmas), washup liquid/dishwasher tabs, bin bags, washing powder, cleaning spray etc. Firelighters and matches, nightlight candles or dinner candles.
And any personal toiletries that the family may need - toothpaste, toothbrushes, shampoo, shower gel, bubble bath, deodorant etc. (It can be handy, if you have the budget, to get these in an internet shop as it saves you carrying them, and any other bulk or heavy items).
Do you already have, or need, things like kitchen foil, cling film, greaseproof paper etc?
Paper napkins, paper plates, plastic glasses?
General basics - cereal, bread, butter, jam, fruit, breakfast juice, eggs, tea, coffee, hot choc mix...
My list (I don't have to buy it all - I go through this to see what I have and what I need - and I don't need all of it every year)
Fridge:
Milk
Butter
Cream
Crème fraiche or sour cream
Cheese
Eggs
Rashers and sausages
Turkey or Xmas Day joint
Any other meat for next week
Smoked salmon?
Cooked meat for sandwiches?
Ready to roll croissants or pain au chocolat for Xmas Day breakfast
Nibbly bits to snack on (mini quiches, sausage rolls etc)
Freezer:
Prawns
Ready made pastry (puff and filo usually)
Fruit & Veg:
Lemons (for slicing in drinks, squeeze over salmon, but also for making hot lemon drinks against colds that threaten)
Oranges or grapefruit (to squeeze for brekkie)
Lime (we always have fajitas over Christmas one day)
Apples, Bananas, ....
Clementines - Christmas treat
Grapes (cheeseboard)
Onions
Garlic
Carrots
Parsnips
Brussels sprouts
Peppers
Tomatoes
Leeks
Cauliflower
Lettuce
Mushrooms
Courgette
Avocado
Potatoes
Herbs: Parsley, thyme, tarragon, sage, basil, chives
Cupboards:
Tinned condensed soup (tomato, chicken & white wine, mushroom)
Mayonnaise and Ketchup (need both to make Marie Rose sauce)
Pasta, rice
Couple of jars of pasta sauce and curry sauce - nice ones for leftovers
Fajita mix and wraps
Salsa
Gravy mix
Biscuits (I usually buy a couple of nice packets rather than a tin - less waste)
Crisps
Soft drinks (plenty) and sparkling water
Tonic (to go with my gin)
Wine, beer
Roasted peanuts, pistachios
Nice bitter marmalade
Honey (for lemon drinks and over roasted root veg)
Part baked bread rolls (for fresh bread on Boxing Day)
I usually have breadcrumbs in the freezer to make stuffing but may need sausage meat
Baking ingredients - (I normally have these but make sure these essentials are in - for cookie making mainly)
Flour
Unsalted butter/margarine
Caster sugar
Vanilla extract
Icing sugar
Mince meat
I've probably forgotten loads but hopefully that helps a little.