The title is a bit over dramatic but, per the title, if you could contribute with one piece of knowledge to a book that every single individual should learn from in order to kickstart a civilization, what would be yours?
My personal choice would be the process of soap making, from scratch.
Electronic valves are still a thing?
I had relatives that swore on radios based on that technology could endure the detonation of bomb and still work flawlessly.
And I had a colleague in school that saved up to be able to buy a valve based guitar amplifier.
They didn’t stop working somehow. The trick is that they need a very high (deadly) bias voltage to work, are mechanically delicate, have to be heated and possibly cleared of gasses leaking in, and from what I can tell have inferior characteristics for a lot of applications.
On the other hand, your relatives are right about the electrical toughness, and they have no firm upper frequency limit, so they still have industrial niches.
Yeah the guitar amp and vintage HiFi markets keep a few types (mostly power triodes and pentodes but also preamp valves and even a couple of rectifiers) in production, largely in the former Eastern Bloc. There’s a few people on YouTube making their own too.