Survivalism automatically gets a bad reputation by sticking that ism on an otherwise fundamentally reasonable idea; after all if you don’t survive you aren’t going to be doing anything else, and in a larger sense if humanity doesn’t survive then it isn’t going to be doing much of anything either. Back in the 1950s the US government got interested in the idea and supported a lot of fallout shelter programs. This was mostly done on the cheap by putting up signs pointing to local public basements where some water, and leftover WW II food supplies were stored. That may have made some sense up until about 1965 when our possible enemies had so many H-bombs that no one in an American city was going to survive anyway. The US and USSR then gave up on the hope of surviving, and went for a mutually assured destruction policy, (MAD) for short, and the world has lived precariously on the brink of Doomsday ever since.
Some other countries like England and France seem to have hoped that having only a few A-bombs would make everyone hesitate to attack them while appearing not excessively threatening. Switzerland has had a policy of making their country extremely difficult to conquer by having methods of dispersed heavy weapons made readily available to the public. Thus, even if an army were to move into their country they would have to fight a guerrilla war faced by an guerrilla army equipped with very sophisticated weapons, and not just improvised explosive devices (IEDs).
There are some survivalist groups with newsletters, and blogs such as survivalblog.com and Survive Club which I am in basic agreement with for disasters up to DISS~9 (Click here for a nice printable PDF DISS~ chart.), but beyond that survival in the Northern Hemisphere where most survivalists seem to live is improbable. However, if anyone does survive there, it will be some of these well prepared people.
My basic approach to this survival of humanity problem is that when WW III starts everything living in the Northern Hemisphere is dead, and only those in the Southern Hemisphere have any chance whatsoever. If it is a particularly bad conflict where most weapons are actually exploded then going south is one’s best hope, and the further south the better. Southern Argentina and Chile, become the last to die or to put it a bit more positively the last to survive. The graphs resulting from that major war would look like this:
Note that in this scenario the quantity of food tops out and begins to decline before WW III begins. This graph postulates a Doomsday of DISS~10 or 11 with quite a few people surviving, but they will probably be only those very far south. The people, even the prepared survivalists, in the Northern Hemisphere will be under a dark cloud for over a year, and will have no new crops, and no new food. That combined with all of the other problems will probably make life in the Northern Hemisphere unsurvivable. The most realistic plan for decent survival of humanity in the one hundred year, and beyond range is the Lifehaven strategy of setting up large storage facilities filled with recovery materials in remote Southern Hemisphere locations.