Fresh greens, fruits, and vegetables are often left out of a camping diet, but once you can identify a few wild edibles you'll eat much better when camping. If you've ever thought about eating wild edibles but didn't know when to start...the best time is in spring.
The field guides we use for wild plant identification are:
1) "Edible Wild Plants (Eastern/Central North America)" by Lee Allen Peterson, part of the Peterson Field Guides series
2) "Field Guide to Edible Wild Plants" by Bradford Angier
For general plant identification (non-edible) we recommend:
3) "National Audubon Society Field Guide to North American Wildflowers (Eastern)".