I don't recommend carrying a 'pocket guide' if you intend finding, identifying, and eating when out and about unless you are already experienced.
Study the subject using good quality photographic guidebooks (by all means use a pocket one to remind you) then, when you know you can identify certain species for sure (without a book) you're ready to forage. OK, there are certain well known edibles that you don't need a book for but I urge you to use good books for identification first before foraging. The quality of the photos and drawings in the pocket guides is often just not good enough - and some, like Food for Free, contain mistakes.