Go to the Asteroid Belt and find nice valuable rocks and volatiles floating around. No need to expend Delta-V to land and take off. Even the big asteroids have minimal gravity. Really though, what we need to concentrate on is finding habitable extra-solar planets and send some probes there. Earth may be a burnt cinder by the time we hear back, but the longer we wait the longer it will be. Inhabit the Solar System and then move out, even if we get there and the planet is a dud we can live in space indefinitely.