I used to be the residing edible plant "guide" on native plant society hikes when I lived in Oregon. Of all the books I have on this subject matter - and they are many - my favorate is: Discovering Wild Plants by Janice J. Schofield. This covers the plants part very well. It helps also to really know your plant families. Some families have both edible and deadly plants in them, and mistakes are often made in distinguishing which is which. Make absolutely sure you know what you have. One mistake could be your last.
As for mushrooms. The above statement is all the more true for mushrooms. I have helped ID mushrooms for local mycology groups and have been an avid mushroomer for years. I still double check everything, sometimes triple check. The best book for learning mushroom identification skills is called Mushrooms Demystified by David Arora. I highly recommend contacting a local mycolgy group to learn id skills and to have someone who really knows what they are doing be a back up identifier. And that said, even when I learn of a new to me potentially edible mushroom by the head identifier of our local group...who REALLY knows his stuff, I still look it up for myself and key it out and take spore prints and the such.
Going out mushrooming with someone who knows there stuff fairly well is a good way to start learning. There is NO room for mistakes in mushrooming. Mushrooms are far more difficult to identify than plants. Some can only be fully identified by looking at the spores under a microscope. There are easy to learn edibles and easy to learn deadly mushrooms. And this is a good place to start. I just can't say enough about not assuming anything when it comes to mushrooms. It is a constant learning experience and a rewarding one, but always err on the side of caution.