Agree with the 'Trees' & 'Food for free'. I also have the 'Mushrooms' copy which is useful if you have a background knowledge, but not enough on its own to be 100% in ID.
I keep getting tempted by the 'Seashore' one and am only holding back as it doesn't state if a species is edible or not.
They are fab little books, and because of their size it is so easy to keep in the bottom of a bag so they are always with you.
j