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.
I think in a way religion was a necessary component in managing populations.
Without education humans will naturally look to “organised luck” or supernatural deities for meaning. That can be used as a kind of carrier wave to disseminate basic information.
“God says you should clean your cock and balls once a day in order to bring good luck”