#1-Overview
The natural Holocaust scenario that has been suggested is not very dissimilar the many nuclear holocaust scenarios that had been presented in works of fiction not that long ago. One author, Johnstone, had quite a following here in the USA that had taken his fiction somewhat to heart and had created a loose-knit band of groups who are preparing themselves for such an eventuality. I believe this group has a website.
Firearms are, and still will remain, a viable protection system here in the USA. I refer the reader to the "updates" I have posted in the 'Forum-Politics & Society-Weapons' thread. I should also point out that the historical re-creationist groups of the Fur Trade era and the US Civil War era are better equipped should there be a shortage of smokeless gunpowder and primers. You do have your own 6pdr gun w/limber and caisson don't you?
Rambling on...
During the 1970's, here in the USA, the "back to the earth" commune concept was put into practice and alternative energy and dwellings were all the rage especially in the State of California. Few of these "communes" still survive, their failures being traced to too much 'deadwood.' This will be a common concern for groups placed into an emergency survival situation without planning aforethought.
Sanitary waste, processed by methane generators, may produce fuel for cooking, lighting, heat and for the operation of diesel-powered electrical generator units while providing a high quality fertilizer slurry for a sustainable agra/aqua-culture system. Home bio-diesel 'plants' are viable fuel sources as well for there are many surface alkali flats in the desert regions of the western and southwestern states. Fiber optic light pipes, providing UV free sunlight, have been shown to produce both larger fruits as well as increases in production yield.
There have been sufficient philosophical crossovers of both back to earth and survivalist groups such that the amalgam of an armed tribal survivalist/alternative resource community may now exist but the integration appears far from complete and it is doubtful that any of these groups have developed, to the best of my knowledge, a 100 year plan.
Nomadic hunter-gatherer groups may survive in the short term but with the prospect of a 'nuclear winter,' as indicated in the initial scenario, it would be most difficult without a sufficient stock of woolly mammoths.
On the Religious front; some 'Mormon' groups have a 1 year emergency subsistence home stock pile requirement which places those groups on the highly probable survivor list.
One's survival toolkit consists basically of the will to survive, adapt and endure, the available knowledge, then available equipment/resources.
