OK, I am assuming that you need everything, you are doing a shop to cover 22-26th (breakfast 27th?) at least.
So when you add in all the small things like salt and pepper, herbs, butter, olive oil, tin foil, cling film, bin liners, washing up liquid, matches etc, breakfasts, snacks, lunches, dinners, treats - yes it does add up quickly.
When we travel to SC places, even at Christmas, we have a big spend. But I do tend now to bring a few things from home (we drive so it's easier, but some things could be squished into cases if travelling by plane/train etc.
A 100ml squeezy bottle of washup liquid gets through a lot - especially if its a decent liquid like fairy (not the cheap watery types).
I have a set of glass salt and pepper mills from the supermarket that I keep in my SC box - they were only cheap but they save on buying every time. I usually bring a few things like a handful of stock cubes and some gravy powder in a plastic tub or small sandwich bag (the Ziploc kind) rather than buying a whole fresh box. And I slip a few bin liners into a pair of shoes rather than buying a whole roll on arrival.
I DO make sure to get loo roll (although I always bring a roll in my case too), and a pack of kitchen towels really make sense at Christmas time - but the basics types are fine.
The other thing I bring is a few tools, as often there are key ones missing. THink carefully about what you normally use, and really would miss - corkscrew, a good sharp knife, a wooden spoon, a veg peeler, a whisk, a set of oven gloves, a teatowel or 2, a small proper chopping board (mine is plastic). I have a SC/camping box with my "travelling tools" in it, and have put a few into my case when flying if I am unsure of the facilities.