Reddit mentions of Botany in a Day: The Patterns Method of Plant Identification

Book, here is one you can afford,

http://www.amazon.com/Botany-Day-Patterns-Method-Identification/dp/1892784157

^This is good advice. This book is really helpful for learning basic plant families and such. Start with this and a good color-picture field to your area and you can ID damn near everything you find. To be fair, theres a huge number of plants out there that are of no or only marginal use to humans, so ID'ing them won't help your foraging. Its just fun!

Not all books, but if I had to choose only 5, these would be them:

• "Possum Living" by Dolly Freed (living very cheaply)
  
• Botany in a Day (pattern method of plant identification)
  
• Dmitri Orlov's Blog (creative solutions to housing, skills, self-employment)
  
• Deconstructing Dinner (Best radio show on the food system and the models rising to replace it)
  
• When Technology Fails (here because it's such an empowering book, shows you how to do everything yourself if you ever have to.)