Have a good look at the tinned food in Sainsbury's or M&S - chilli etc.
There are some breakfasts in pouches, too - sauteed potatoes, bacon and onions.
And a range called 'Look what we found' which does excellent main meals that don't need chilling. Not cheap though.
If camping in a big group we usually take a pre-prepared casserole type dish or curry for the first night, a 'one pot' dish that can be heated over the stove. The BBQ the second night.
Herta frankfurters are good to heat in boiling water for a hot dog.
Take lots of fruit like satsumas to ensure some healthy input. And cherry toms.
Actually we are ambitious with our BBQs and do corn on the cobs, asparagus, have a BBQ wok in which we can do marinaded mushrooms, felafels, 'squeaky cheese', and we always have a campfire and do baked potatoes in the embers.
Take a pack of wraps or chapatis, put them in a frying pan on your stove, grate on cheese, add a slosh of bottled sauce (such as Lloyd grossman pasta sauce or even the tomato salsa dip from Doritos) cook, then flip over and cook again - for quesadillas.