Great game, although i am pretty sure that in the event of an actual zombie apocalypse, pretty much everyone would know to call them zombies, not drifters or roamers or walkers.
to kill cashier, get pistol, go up close on his side of the counter, get to where, if you shoot at his feet, you can hurt him, yet you are too close for him to shoot, then just shoot until he is dead. + to keep alive!