As always, let me play Devil's advocate, here. We have historical precedents for the collapse of civilization, such as the fall of the Roman Empire. For a millenium we lost the secrets of indoor plumbing, and how to formulate concrete. But most of the base skills remained in the peasant population: how to plow a field, forge steel tools, lay brick, work wood, set a bone, drive a team of draft animals. How many of us know how to do any of these things today? And if we do know one, how do we trade the fruits of that skill with others who might have other crafts. Post apocalyptic scenarios imply no governmental control or social organization. Even the Roman Empire did not collapse overnight, and feudalism, the form of social organization which usually takes over in tough times, had time to adapt itself to the new conditions.

The only thing I personally know how to do which might be of value in a post-apocalyptic scenario is navigate a boat, but I don't know how to build one, or loft a sail, or braid line, or make a fishnet, or any of the associated technologies which have to be be coupled with mine to help rebuild civilization. I understand the theoretical chemistry of smelting ore for metal, but I don't really know how to start a fire without matches.

In the past, when an empire collapsed, all the skills survived except those which required high levels of social organization. The average peasant might not have the architectural skill to build great monuments, but he could build shelter from the weather for his family. We are characterized today as a society where people don't know how to make soap, or cheese, or even their own clothes. These were skills most housewives possessed a century ago.

I don't think technology will survive, except maybe in places like India. I think it will all go back to the neolithic, or even earlier. When we run out of ammo, we won't start making bows and arrows; we won't know how! We'll just swing our rifles like clubs.