Zombie Apocalypse.

You break into a building and steal as much fuel as you can carry. You pick out some vehicles lying in the streets that have suffered the least amount of damage with the keys left in the ignition: A pick up truck and a van.

You fuel it up, and drive to a surplus store for more ammo and weapons, a grocery store for more food and water, and several other generic stores for materials that you can use to barricade.