That would be the mighty Cattail (Typha spp.). It shows up in survival books frequently because it can provide a wealth of resources: shelters, bedding, fire-making tools, and food. I will walk out of my way on a survival trek to obtain cattails.
During the winter and spring months, we collect the roots (rhizomes) and roast them on the fire until charred. Then we peel back the outer rind and snack on the starchy interior. This is one of my favorite foods. During the spring, we gather the young shoots and eat them raw or in a stew. The yellow pollen, available for only a few weeks in June, can be mixed in with regular flour to make a protein-rich bread or pancake mix. The leaves are also fantastic for weaving into a strong rope.
Whatever you do when it comes to harvesting edible wild plants, be 110% sure you know what you are picking and putting in your mouth. Be dead sure you know your plant identification skills, or you could end up dead. One plant--poison hemlock (the same hemlock tea they gave Socrates to drink for his "political views")--is so deadly that just a taste of the leaf can kill you. There is no room for error so make sure you identify what you are picking and sending down your gullet.
Lastly, don't collect cattails near roadways, highways, or ditches with runoff. Even if the plants look healthy, they may be contaminated with hydrocarbon emissions or pesticides.
There's no substitute for taking a hands-on foraging class, so I would recommend looking into the offerings of your local community college, nature center, or arboretum to see who is leading field trips on edible plants.