For years Anna Comstock's Handbook of Nature Study has been an essential tool for all budding naturalists but its large size made it impractical in the field. It has now been broken up into individual sections for easy portability. New full-color photos are included for those times that you're unable to see nature up close.
This volume only features the introductory sections from the other volumes. If you have the others this is not necessary, but can be handy.