Dining on wild foods is something to be taken seriously since one mistake with a toxic plant can be deadly. Learning to identify and utilize edible plants is best done with a reputable field guide and by taking a class with an instructor versed in the use of wild plants.
I prefer field guides written by authors who actually incorporate edible plants into their lifestyle rather than botany-type reference manuals. In that regard, here are some of my favorites:
Eull Gibbons classic work, "Stalking The Wild Asparagus." Eull kicked off the edible plants movement back in the 1970's with his informative and passionate writing about the wild meals to be had in your own backyard and city.
Chris Nyerges, who teaches edible plant workshops around Los Angeles, has a simple, how-to book-called "Guide To Wild Foods"-that covers the basics and is perfect for beginners.
The "Peterson Field Guide to Edible Wild Plants" is a good all-around book covering the common edible and dangerous plants found throughout North America. Also, check out the "Peterson Field Guide to Medicinal Plants and Herbs".
"Edible and Medicinal Plants of the West" by Gregory Tilford is worthwhile for its detailed photos of plants which show not only the flowers but stems, fruits, and leaves.
I would recommend starting with one or two of these books and then looking into a class at a local arboretum, outdoor center, or university to get in-depth training in identification and usage. Some of the more common edible plant resources I have my own survival students gain familiarity with are: dandelion, acorns, pine nuts, and cattails, so consider starting out with these and building on to your plant knowledge from there.