Deadly Days

The easiest way is to aim for the rocket ship ending, make sure the mission you choose contains the last part needed, make sure you only have enough food to feed one survivor, if not, level up repeatedly until the requirement is met, once you have started the mission, go straight for the rocket part, don't scavenge for anything else, once you have the part, go back to the bus, start the engine once you get the chance to do so. All but one survivor will starve the next day, and the rocket should be ready, when you are ready to proceed, open up the mission's tab, there should be a mission with a label that says something along the lines of 'launch rocket', choose that mission, after the rocket has launched, you would win that run, then unlock the achievement 'Sole survivor' if you haven't already.