There are far more than 13 wild edibles you can find in the forest...however, finding wild edibles and eating them are two entirely different things, especially if you have never eaten them before...your body needs to go through an adjustment period...if you just run out into the woods and start eating a bunch of edible wild mushrooms for the first time, you could still get sick, it just won't be of the toxic variety...
This book was a fairly good read, especially for the novice outdoor enthusiast...it really doesn't matter what kind of outdoor activities you enjoy, you owe it to yourself to be properly prepared for the absolute worst at all times...not too many people get lost, or have an accident on purpose, when they're out in the woods hundreds of miles from the nearest help...[you may need to find food (http://gear.survivalist.com/survival-food) in the forest just to survive...!