Part of the ten essentials is extra food. Many Scouts and other explorers have had their adventures extended. Those that packed extra food faired better than those who didn't.
There are a number of poisonous plants in our part of the world. Some will make you very sick and others are lethal if consumed. It is far easier to learn how to identify poisonous plants than it is to correctly identify all the edible plants in an area.
We cover this topic in greater detail on our Poisonous Plants Page
Universal Edibility Tests can be found in military manuals. They sound like a neat tool to have in your survival repertoire, but the true of the mater is that there is NO Reliable Universal Edibility Test. Using this tool can get you killed, even with access to advanced medical care.
The Universal Edibility Test is something to consider as a last resort when a military pilot is stranded behind enemy lines long term (30 plus days) and is starving to death. Most lost Hikers and Scouts are found within 72 Hours. 72 Hours is not enough time for you to starve, but is enough time for you to die a horrible death from poisoning.