That's a long time. I'd take lots of food with me and don't worry if you have some left over.
I'd suggest taking a bag of apples, carrots and bread. Cheese or egg sandwich. At the very least.
I'd probably take more than all that though.
Take a hot drink like a thermos of tea or hot water for making coffee. Unless you want to buy it on the road.
But there's plenty of things you could take. When i'm travelling with no refrigerator for months, i will cook spaghetti the night before for dinner and half of it will be for lunch the next day. In it i would put olive oil, can of good tuna you like a lot and parmesan cheese, garlic and good black pepper. at least 100g of dry spaghetti. Its really not so bad at all cold so long as you don't over cook the pasta.
But i find lots of things we usually eat hot are fine when they are cold when that's all there is.
You could also have hot soup in a thermos if your thermos is any good. Otherwise it might end up being just warm.