I was going to comment on the fiddleheads in the first post, but it looks like someone beat me to it! The ones pictured look more like bracken ferns, which contain a lot of carcinogens and other bad stuff. In NH/VT there are like 4 or 5 different types of ferns that all look somewhat similar. The dead giveaway that one is a ostrich fern is, as one member already said the "U" shaped stems, and the papery material coating younger fiddleheads. Boiling ostrich ferns in a change of water is optional, it will help the taste (most people compare the, to a combo of asparagus and broccoli). I can tell you right now, my favorite way to eat them is pickled.
To pickle, first blanch (drop in boiling water for a couple of minutes) the fiddleheads.
Next, mix your pickling concoction (vinegar and pickling salt, spices if you choose, google for recipes) and bring to a boil.
Remove the fiddleheads from the boiling water with a colander transfer them to a jar, pour the boiled pickling juice on top until the jar is full.
After capping the jar, place in a pot of water up to the base of the jar lid, bring this water to a boil.
A favorite wild edible of mine besides fiddleheads is queen annes lace, or wild carrot. It is easily confused with hemlock, which is poisonous. The way to discern the two is that the root of queen annes lace has fibrous growths, whereas that of hemlock is smooth. Queen Annes lace root will also have the distinct smell of carrot. Here is a picture of a mature plant:
Recently I learned from a blog that the inner bark of the Eastern White Pine is edible, and very nutritious at that. Apparently it was a staple in the diet of the Adirondack people, in fact the name Adirondack means "Bark eaters"! The eastern white pine is huge, they grow hundreds of feet tall and have a maximum girth of eight feet. The needles grow in clusters at the ends of branches and are three to four inches long. The bark of young trees is smooth, green and shimmers. The bark of mature trees is gray and very rough. Here is a picture of the pine needles, the most easily identified part of the tree:
As with most north American coniferous trees, it is very rich in asorbic acid (vitamin C), and as european explorers were dying of scurvy in the forests of the new world, they were literally surrounded by a sea of the nutrient they needed to survive.
The inner bark is fibrous and slippery, and is best pan seared or seared on a rock on top of coals.
Another wild edible i just remembered while reading the cattail post: japanese knotweed, or mexican bamboo as it is sometimes called. The young shoots are edible before they become too woody and fibrous to eat, usually around 6 inches and under. Knotweed is a noxious invasive weed that propigates by underground root systems and rhizomes. Basically any part of the plant, if cut off can grow into another plant, so it is easy to spread around. That is a bad thing because it out competes local plants such as cattail and replaces them.