This is from backpacking experiences but I have a similiar low-to-no cooler plan.
Lentils and Rice, spice it up with a dried vegetable soup packet (soak in water for ~10 minutes first) and it makes a really great burrito/wrap with some hot sauce.
Dried mashed potatoes always works well to carb up if feeling low
Tuna packets and the like (I like these more than cans as less waste and packs down
Peanut Butter and honey on tortillas (I eat almost everything out of a tortilla)
Seven bean soup mix is readily available in most stores and all it needs is water and some time.
Also if not vegetarian things like a beef boullion cube can really add a nice taste to otherwise bland rice or beans concoctions.
