Fats and Omegas. Some tuna comes prepackaged in sunflower oil. Carry an olive oil to add to essentially everything out there, and aim to get healthy fats when you get to town. Your body will be screaming for carbohydrates and starches, aim to get those from everything BUT sugars where and when you can.
I returned from a thru having lost 25 lbs, and foolishly neglected to put the weight back on afterwards. My thyroid gland did not take kindly to the long-term weight loss and I developed an uncomfortable and permanent nodule on it. Now that I am eating fatty foods again my health is being restored.
Maybe a little TMI but certainly some realities of trail food and LDH body mass. The body's organs don't normally give outward warning before they tip over and fail.