There are lots of things you can do in the car instead, we could burn natural gas, we could load up the car with batteries and battery technology gets better. For airplanes there aren't too many alternatives right now. And so we have to be thinking hard and planning for what actually does happen, not 10 or 20 years from now, but 30 or 50 years from now, to replace this incredibly useful and convenient source of energy as a fuel.
So planning for the end of oil means innovating... It's not planning in a formal sense, but it means innovating and developing new ideas and new technologies, which 30 to 50 years from now could be the basis for radically different primary energy supply.