What kind of foods do you like though ?
Rat packs are hard to beat for convenience, variety, and long lasting stuff, just in case in the car. Having said that though, I'd rather pack a decent box with stuff I know I'll eat.
I can happily visit Home Bargains and stock up on their sealed bags of fruit like dried mango, apple rings, mixed nuts, jerky if it's stuff you like....visit Sainsbury's next door and they have bags of pieces of crunchy baked cheese

all the protein, a little lower on the calories, but it doesn't need a fridge. Near as daughter in law loves the peeled roasted chestnuts in those sealed bags too. Usually pretty long dates on all of those too.
If you have the wherewithall to heat water, some spoonsful from a bag of mixed fruit muesli, couple of scoops of dried milk, and there's a hot porridge breakfast.
Instant noodles are quick, pretty bombproof really, and filling. Add in some cuppa soups and some of those vacuum packed mini naan breads....
I think it comes down to what you want to eat.