They most certainly are not. If you're buying unhealthy food only as snacks, you mistake your subset as all unhealthy food.
If you need calories and are on a shoestring budget, your options are potatos, bad bread, Coles cakes etc. You can eat for a week on a few dollars but you'll become overweight and eventually die of malnutrition. Your options become even more limited if you don't have a working stove due to being cut off your gas.