Take pringles - they have so many different uses. They can store your drugs, delicious crisps, AND then you can piss in the tube when you’ve finished the contents.
Bog roll, bin bags, wipes, suncream, lots of socks, proper decent boots (not wellies), waterproof coat. I usually don’t take a pillow to save space then regret it.
Cans of food that can be eaten cold, those horrific sausages and beans in tins etc. Just get it down you.
Beer. Tactical car parking if possible to allow returns. I used to just ignore the wardens when going to Reading to park alongside all the camping, I think it has changed now.
The first to have a large capacity, wide rim and secure lid. This is for pissing in when you’re in your tent in the morning/night. The biggest Copella ones used to be good for this, until they narrowed the rim diameter
The second to have a squirty-type cap. This will replace toilet paper through the weekend. Fill with water before entering a bog and use to spraywash your arsehole. Works a treat.
I always take individual juice boxes of juice (for brekky drinks) and chocolate brioches (the kind that are individually wrapped)
If I have access to a camping stove those pouches of things like chilli or stew are pretty good - maybe bung in some tinned new potatoes or that rice that comes pre cooked in pouches - pouches are a good call all round as they weigh much less than cans