I live just outside a small town. Our subdivision and town have a history of helping each other during emergencies. My block has had a lot of new people move in though that we don’t know that well.
Now that you mention it, we could probably prevent traffic from the big city, but then that would also destroy the ability to transport supplies especially medical supplies.
But, if you have prepped right, you have medical supplies. I’m a nurse, on one of my prepper neighbors is a surgeon.
In our group we also have a mechanic/machinist, a former Nam-era Green Beret, a two former 101st airborne soldiers. We also have a farmer, an chicken raising outfit, and several lifelong hunters.
Additionally, I’m a ham radio operator and fireworks buff. I can make blackpowder and flash powder, essential ingredients in making field expedient explosives. I also am a lifelong reloader, with enough ammo and ammo-making supplies to fight a war. ;-) In our network, we figure we can arm and supply 50 people for 2 years.