OK, so technology is a veneer over the harsh realities of life and were it stripped away we would all have to revert to living as we did for millenia. But as you say what you carry in your head is yours to keep. In a long term scenario (really long term) where the infrastructure that makes it possible to buy a replacement ceramic filter cartridge for my gravity fed filter has been renedred useless. (asteroid impact, holocaust etc. - (btw this steps out of the scope for this site sorry)) You will still be quite a bit ahead of your ancestors since you have an opportunity to understand basic hygene. Something as simple as washing hands and burying waste is responsible for increasing life expectancy by quite a lot. Before the cow-pox vaccine quaranteen was used quite-effectively on a community scale but nothing could be done for the individual to protect against small-pox other than hand-washing and face masks. Both of these ideas are very new. No need to face a total reversion. Basic individual survival skills are only the barest beginnings of what you want to take in your head into a long term survival situation. Community sanitation, water purification, waste management, smelting and smithing, basic electronics such as how to build a generator etc... would be as necessary an addition to your mental preparations as the knowledge of how to build a fire with friction. After all how many generations do you want to wait before your descendants have electric light and central heating?

As you note we have wandered quite far afield.