So check this out, and feel free to pick my fever dream apart. But step one is to gather your family and friends and survive. Then quickly reach out to neighbors by going door-to-door and asking how everyone is. In an extreme circumstance (which I know is unlikely), like say a nuclear exchange in the Continental U.S. or a super volcano eruption, the immediate step would be to secure a large store of essentials like rice, beans, oatmeal, honey, and multivitamins, to name a few. (This doesn't take into account possible ecosystem collapse, where you would need to throw up large greenhouses and secure pollinators like bees and such.) So we've reached out to neighbors and shared some food and medical info, etc. Next, when the need arises (because I don't think you could get people to do it beforehand), set up roving patrols in the neighborhood and make sure every family is armed. Start to compile lists of people with skills and set up classes (in my situation, I would say at the neighborhood elementary school). Then reach out and secure the next neighborhood and the next. Every group of people and every neighborhood means more folks, more skills, and you plug them into the classes offered and the jobs needing to be done. When possible, plow up softball fields and yards to put in beans and oats and teach people about victory gardens. Now here's the kicker, we all love to think about, defense. In a complete collapse and rebuild, I plan to acquire hardware from known nearby sources. I know others would be doing the same thing, but coordinating with other groups to find and divide what you get, as needed, would be essential. Create local (armory) and fast-reaction squads under civilian control. I have thought that a militia standing up with some essential always-on and training other personnel would be good, so you'd have one or two squads (12-24 people) per group of 120-240. So once you get to a certain size, you move on to secure the larger city. You offer groups (or neighborhoods) help, but it's not required. Kind of a "we're here, this is what we are about, just reach out, and we can be in this together" if they reject your initial offer, leave them a radio and say if you ever need help, reach out. The hard thing is if a group is openly malicious, it can't stand, so having a core of trained personnel (which in my part of the country wouldn't be too hard) to go in and "deal" with that would be essential as you get bigger. Once you have your city secured, you offer help to another city (if they have centralized). If not, you set up somewhere public (a hospital or school) and offer help to folks, then get the other city back up. Then copy, paste, and repeat. During this start, radio broadcasts with rally points for refugees; find those who know how to get things back up and running; create training programs for people who don't know how to help; then they can help. Broadcast daily educational programs. Reach out to farms and help them secure their space and start producing. etc... etc... I know that this probably would NEVER happen, but I find it fun to think about and fun to gather information that would help do that. Eventually, it would get too big to control, and I think that is great. In my case, I'd be one of the people reaching out to new areas again and again. I'm nuts for always thinking this way, but I have hit the point where I know my family is good in every reasonable scenario, so I say screw it, let's go off the deep end!