This is something that I have put a lot of thought into and there is an end result. Basically there are two situations that you have to consider:

1) The economy / government has eroded and lost control. Crime is soaring but there is still commerce in one form or another. Essentially a wild west type of environment.

2) Complete social breakdown. No law, no morals, worst case scenario.

The first is honestly the most likely due to the current hoards of completely dependent people. In this scenario there is a chance for groups to form, but they are only going to be successful if they fall into one of two categories:

1) They are all like minded prepared members that respect and trust one another absolutely.

2) They have no other option for survival so they band together for strength in numbers.

The first is like an old west town, the second is a common street gang. Chances are these will be the two groups in competition for resources. There are combinations and other options, but this as far as I can tell is a fairly comprehensive breakdown. With that said, the only way that a group will survive is if their environment falls into the first category of both conditions. Other than that it will be impossible to keep people together for any length of time.

The only real reason to have a group is self defense. Trade / bartering can be conducted with anyone, provided you have the means of defending yourself and your property. The real threat is being overrun by a larger gang type group. Sure it would be nice to have someone that you trust to trade with, but on a long enough timeline you will have to venture out of your compound and trade with others, and for hunter gathering type activities.

But for me it all boils down to one absolute, and that is that you can only trust family. My family has had this mentality for some time now and everyone is diversifying into very specific skill sets. I am electrical / mechanical engineering, one brother is a physician, my dad is former special forces and great at killing stuff and my sister is a cultural anthropologist... (there is always one in every family that just doesn't get it.) We all hunt and shoot and we all prep as best as we can.

I still have a group of friends that I plan on banding together with in order to make an initial stand if need be, and to travel to my families planned meeting place (we all grew up together and our families live close). But I do not plan on having them be a formal part of my group. We will all protect our own families and work together as needed, but to attempt to form anything beyond a loose community is frivolous because everyone has their own priorities that will always come before your priorities. This is not to say that I would not help my friends and their families if they were in need, but to pre-establish a community will be a lot of wasted time when it falls apart.

After a certain point it becomes clear that planning can only go so far because the possible choices that you will encounter are too numerous and lead down too many diverging paths. The one thing that I would throw out there as the most important aspect of this whole topic is to have a planned meeting place for everyone in your family that you care about. Then they are individually responsible for ensuring that they have the means to get there. If you put enough preparation into this location everything else will fall into place as best as it can depending on the choices you make.

If we are lucky enough for only a short term loss of government / economic collapse then communities will form and there will be opportunity to redevelop society as we know it hopefully purging liberal ideals for a few generations. If that continues to fall into complete social breakdown you end up with a 5 seconds after situation where you can expect 80 - 90% of the people around you to die and that is something no group can handle and remain organized. No amount of preparation can change the path of a community subjected to that level of disaster. It will be all by the seat of your pants decisions that people will make because they have no other choice. The strong will live, the weak will die.