I'd say one of the best sources for cheap calories has to be fast food. Check out the McD fries in this experiment:
So....What? No one has told you, that you eat nuked food down there? If your fries has been nuked, then deep freezed, then fried in oil at 180°C, there cannot be any germs, not anything living in it, so it just dry out. In fact, that is the secret of those McD fries: there isn't any moisture in them, just some oil, so how there could be any fungus etc. if you leave them in the sterilized jar?