People eat differently over the holidays
On an average week we are a house of 2 adults, one child and one baby. We have cereal or porridge for breakfast, cheese/ham/egg sandwich for lunch with some fruit and protein/veg/carb based main meal. We can make a chicken or joint of meat last 3 days. Snacks on between meals are crackers, toast, fruit and puddings are fruit and yoghurt. On a typical weekend we go through 2pts of milk, 3l of oat milk, 1 loaves of bread, 0-3 eggs, 1 meat based items, half a back of cheddar, 1-2 bottles of beer maybe a bottle of tonic.
When my in-laws visit for a weekend with have eggs/bacon/mushroom/smoked salmon etc on toast for breakfast, more elaborate sandwiches for lunch, nicer dinners, make crumbles or pies for puddings. We go through 8pts of milk, 2l of oat milk, 3 loaves of bread, 8 eggs, 2 meat based items. 6 bottles of beer, 1 bottle of wine, 2 packets of sharing crisps, a packet of crackers, 3 packs of various cheeses, a pack of nuts. ..... It will be very similar over Christmas but rather than being with us for 3-4 days they are staying for 10! 3-4 days will be similar to this and the rest more normal eating patterns but still that's 2 extra adults. We eat a lot of rice and pasta during an average week as they cook quicker than potatoes, my mil struggles with pasta so we eat more potatoes. We use frozen veg for speed during a typical weekday and fresh veg in the weekend or when we are at home. Food changes from quick fairly tasty food to taking those extra steps to make it taste really good
I have bought a lot of the non-perishable extra in the previous few weeks and if they don't get eaten they will go in the cupboard to be eaten over time subsequent visits. I've got a Christmas delivery booked for the 23rd which should cover most of food until we go back to work/school in January so 12 days normally my food shop covers 5-7 days.