I make porridge with dried milk (plus hot water) April
My walking food for a day walk is usually a cheese and sandwich spread sarnie and a Snickers flapjack, or a pork pie or cheese and onion pastie/roll. Jam and peanut butter sarnies are pretty filling and, as "fuel", tick all the boxes too. I usually take a flask, come winter or summer because there's something lovely about sitting there with a cuppa and enjoying the views
I don't wildcamp but if I'm being a cheapskate on a weekend away, I'll take double the amount and it lasts just fine for the next day, unrefrigerated.
I've usually got boiled sweets (and usually they're Jakemans Cherry Menthols) in my rucksack and pockets as on the move "snacks".