Salt, tomato sauce, margarine, vegetable oil and tea and coffee. You can take them in little tupperware containers, carried in one big tupperware container.
Also, toilet roll. In case the campsite runs out, but it's useful anyway.
A plastic fish slice and spoon.
If you're having a bbq, then firelighters, charcoal, matches and tongs - you'll likely be able to buy them when you get there, assuming you're not going anywhere too remote.
I think a 3 season sleeping bag means its suitable for all seasons apart from winter. I rarely get cold in mine - even on a camping trip where there was ice on the top of the tent in the morning.
If it's your first time, then a saucepan with a lid can be used instead of a kettle. But I like my whistling camping kettle.
Midge repellant, unless you're near the sea.
An easy one pan meal is a tin of stew mixed in with canned potatoes and heated up. But I quite like cooking out so usually do more.
When we get there, we usually get bread, bacon (or other breakfast stuff), biscuits, milk, a bag of salad, crisps, and, if we're having a barbecue, a jar of sauce of some kind (hollandaise, usually). Plus whatever meat we're getting. And shitloads of booze.