What would your contribution be for a book put together to restart a a civilization?
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.
All these tasty nutritious facts are great, but they're doomed without a robust immune system.
They need to know how there's a drunkard's walk or one-way tropism for wealth and power to accumulate in the hands of the few, how the noblest intents get degraded and corrupted over time, how rich people get to make the rules and thereby get even richer, giving them even more control over the rules.
How this is what killed our civilisation in the first place, and how it will kill theirs if they let it. How you need to water the roots, not the leaves, unless you want the whole tree to collapse.
What rent-seeking looks like, how tribalism works, how propaganda and psyops and PR campaigns work, what narcissists and sociopaths are like, what abusive relationships look like (since they use the same tactics), how to spot demagogues, grifters and think-of-the-children paternalism. How internecine conflict is encouraged and used to distract from actual oppression. How the church maintained a vast grip on power for millennia just by manipulating shame, fear and self-righteousness.
How you can (and should!) make a bunch of rules to slow or mitigate this, but cancer finds a way; it will worm its way past your defenses in time. And when it does, you can't fix it from within the system, pretty much by definition, because it subverts the law and the entire social contract to protect and serve itself.
How the only fix is to step outside the law, step outside the system and root it out the hard way, from the top down. You can't put a formal trigger condition on this, as the failure mode will game its way round it: just say that when you need it, you'll know.
There is some evidence presented in David Graeber's last book that Natives of Northeast America already knew all this wisdom after learning the hard way from the collapse of the earlier empires on the Mississippi hundreds of years before white people arrived. Then when we showed up, they went oh no, not this bullshit again.