Well you would obviously begin to acquire books on home methane production from your own human waste for an energy source through combustion, problem number one solved. For food, well if you were fortunate enough to be able to settle down after the collapse, then you could seek out various seeds for plants, such as corn, soy, apples, peaches, plums, potatoes, etc. Problem number two solved. I believe after this would require the accumulation of a social group in which to rebuild a society, a small town even. The Problem with water is to build a desalination machine capable of turning salt water or fresh water into drinkable fluid. I think then the plan would be to just sit back and hope for better days.