In the wake of a truly society-ending event, everything you know will be different. Well, not everything; need will remain. Need always remains. As long as you live you’ll still need food, water, shelter and security. Personal security in the modern era, even in a post-collapse scenario is best provided by a gun. Your wits and your foresight will help you get the other things you need, but it is the gun that will help you keep them after all pretense of civility has vanished along with most of humanity.
Coming up with a gun will likely not be too hard in North America, but the trick will be keeping it loaded and firing. Aside from what people who can handload are able to produce with the gunpowder, primers and other components they have left in their inventory, there will be no production of ammunition, or what is will be greatly limited and vigorously controlled. Assuming you had a stash of ammunition and it brought you this far, it is likely running low.
Where can you look to find more ammo in this scavenger’s economy? What places in the ruined world may have a few boxes of shells sitting in a dusty corner with only the spiders for company? You can absolutely count on any common choice being long since picked over; gun stores, sporting good stores, armories, etc. Where else might you look to find some ammo in order to keep your gun running hot and yourself from going room-temperature?