You got some good ideas there UG.
I've been thinking about that as well and exept for the firearms I agree.
In the US you can buy firearms on every streetcorner but here in Europe it is hard for averige people to get a gun, let alone enough rounds of amo and as I stated before: A bad maintained gun is more dangerous to yourself than to an opponent.
Situating a community near water or a well is almost a must there you're totally right and of course the builders, crafters, trackers etc.
Guys (or girls) that can build transmitters from old PCs or televisions, people who know how things work.
These are good sites:
http://howthingswork.virginia.edu/
Lots of fun too.