There's a reason the military picks one main caliber and makes everyone use it, even if it's not the 'best' platform.
Cops, generally do the same.
Cohesion, should almost be a natural deal within your group. I used to work with guys I didn't even have to talk to. Roll up on a situation, we looked at each other, he went one way, I went the other, or he lead and I covered (or vice versa). Simply put, be able to get rid of the a-hole that stirs up stuff in the group.
Preps depend on several factors. Are you talking bad snowstorm, or CME hit? Bad snowstorm, have back channel coms to figure out who has power, water, infrastructure still up. It shouldn't be a big deal to have your group over at your house to 'recharge' (both them and their 'stuff) until things clear up. After Ida, my wife's whole family met at the FIL's house, I had my generator, he had the propane grill, we didn't even really notice anything for a couple of days and the fuel got scarce. Then we caravanned over to Alabama when it was time to GTFO of Dodge.
CME, well, there's multiple threads on that. You gonna need a LOT of stuff, preferably a welder, a medic, a farmer, all kinds of stuff.