There are two books I would recommend to you to meet your needs. The first is Thomas Elpel's Botany in a Day and the second is the U.S. Army's Complete Guide to Edible Wild Plants.

Thomas Elpel's book is designed to help you identify plants based on the shared characteristics of the different plant families. Each day you learn the identifying markers of a new class of plants, by the end you can quickly tell from a glance what family a plant is in regardless of where in the world you are. Knowing this makes determination of a plant's edibility much easier. For a better taste (ha ha ha!) of Elpel's book check out his website Wildflowers and Weeds.

I think the U.S. Army book will also be useful to you as it covers common edible plants world-wide, not just the northeastern part of the USA.

Hope these help.
-Blast

Disclaimer: purchasing either of those books from the links I posted will result in me earning about 24 cents per book.