I picked up a copy of food for free at the local ‘cheap book shop’ for about £2-£3 but would have happily paid a tenner or more. In all it covers 240 wild foods including fungi, seaweed, shellfish, roots vegetables, herbs spices, flowers fruits and nuts, each with a helpful little illustration to aide recognition. There’s even a calendar at the front giving a month by month guide as to when the stuff is available.
I have the Collins Gem version and the standard version and they are both excellent. The pictures in the gem version can be a little small which is why I also got the bigger size version
There should definitely be a copy of the book in every preppers library