Interestingly, they are generally more nutritious than anything in the grocery store, and generally more prolific. There are many, many books on herbalism, from John Christopher to Richard Schultze to many, many others. Reader's Digest used to put out a coffee table book on basic technology. You really don't know anything, though, until you've been in a full survival situation. It is quite an eye-opener.
Cordage is easy enough to make, but it takes time.
A fishing net, in a survival situation, is an investment comparable to a car. A short listing, which desperately needs updating, follows, of some resources. Absolutely no endorsement of any product or contractor is implied by sharing this info, this is FYI only as examples of what is available. Also, no book can tell you everything. If, for example, you go hunting, you want to do it on an empty stomach, but I've never seen that in any book.