In my experience, the boreal forests provide a slim window of opportunity for obtaining natural plant foods in sufficient quantity to maintain energy. Some of them need to be heavily processed (acorns) and other look and taste good but provide little nutrition (mushrooms, fiddleheads). You have two or three weeks to pick blueberries, blackcaps, raspberries, gooseberries and blackberries etc. You can extend the bounty a little by making teas from various forbs. The good stuff (walnuts, hazlenuts) you will have to fight the squirrels for. Depending on the time of year, you need to be prepared to harvest protein in it's many forms. I don't know where you live, but in addition to Blast's website mentioned above (which is excellent), and a packable field guide which every outdoors person should own, there is Tom Browns book, "A Field Guide to Wilderness Survival". ISBN: 0-425-10572-5. I also found Les Strouds book "Survive" ISBN: 978-0-06-137351-0 very informative. I buy most of my books used for cheap on www.half.com.