Nuts and Seeds are incredibly calorie dense as a snack, or as part of muesli or in anything. Really mucho calories in seeds and nuts very nutrient dense for all those bits and pieces you dont get elsewhere. These are your best weapon against malnutrition. When you eat nuts and seeds you can feel them stopping symptoms in their tracks, I swear. They are what your body is craving and make all that protein digestible.
Whole grains. Porridge. ALL HAIL PORRIDGE KING OF FOODS AND SUPERFOOD!!!!!!!!!!!!!!!!!!!!!!!!!
Pulses, such as peas, beans, lentils and peanuts, are excellent cheap sources of protein and contain minerals likes iron, zinc and calcium and fill pans and pad out a lack of other ingredients. Split peas, barley, lentils. All bloody marvellous, available in abundance for cheap, and if you can bear it, exactly what you need right now.
Split peas, and barley, I love in soup. Semolina and pudding rices should get a spot here.
I confess I hate lentils. I am currently experimenting with lentil and bacon soup because they are good for me and I am a grown up.
You ever get the feeling the hippies were right about some stuff? They were, but pulses alone are unlikely to give you the protein you need, you are probably still going to have to bite the bullet with the fish.