How did Sam obtain all his knowledge about living off the land?
In this book, Sam Gridley learns how to live off the land from a whole bunch of different sources.
When he first heads off to live in the woods, pretty much everything he knows comes from a book that he read in the New York Public Library. That is, for example, where he learns about fishing. He also learns a bit about starting a fire from the man who sold him the stuff for it.
But much of what he learns comes after he gets up to the mountain. He learns some from people (like about how to really make a fire). But then he just figures out a lot of it on his own (like how to hollow out his tree).