Whether or not it is done for immediate survival needs or because it is a trend that has become popular, foraging for food is a concept that is spreading far and wide. Foraging has many benefits; in addition to teaching people to identify and use edible plants as food, it is also giving them invaluable education as to foods that exist outside of the grocery store. It is also cost effective to forage, provided you do so legally without trespassing and helping yourself to someone else's gardening efforts.
Since knowledge weighs nothing and is easy to carry, having a working knowledge of edible plants that grow in your area may help feed you in a crisis. Even if you do not actually want or plan to eat such things, knowing what you can eat if your back is against a wall may help you survive.
An example of a food item that is plentiful in many regions is the common cattails. For centuries cattails have been eaten due to their existence and accessibility around the world. They do not run away when you attempt to gather them and bait/traps are not necessary for their acquisition. They are easy to identify and harvest, and they taste pleasant, so why not give cattails a try?
Cattails are perennials and tend to grow in or near water but that is not the only place they call home. In fact, cattails even grow in the desert. Their growth is quite dense with many of them occupying the same space. Depending on the time of year, most all or only parts of the plant will be edible. For example, in spring you would eat the shoots and in late fall/early winter, the roots (underground lateral stalks known as rhizome) are best.
As far as uses go, cattail pollen and starch can be dried and ground for use year round and even made into a tortilla. The root can be washed, peeled, and cut up then pounded in water to remove the sweet starch and fiber, leaving behind the best tasting parts for consumption. It is also possible to boil them down to a porridge-like consistency then add pollen to the mix, thickening it to form a dough of sorts. Depending on the method of preparation you choose, cattails can come out tasting like mashed potatoes or tender, young shoots can be fried which results in a taste like new potatoes. Pointed corms that sprout from rhizomes taste similar to zucchini or cucumbers and can be broken free and consumed then and there or, as they mature, can be peeled and eaten raw. Ultimately any part of the cattail that is tender can be eaten at any time, be it raw or cooked; if you come across parts that are not tender, discard them.
The trick to getting the part of a cattail you want lies in grasping and pulling. To harvest roots and shoots, grab and pull straight up. When the white base is exposed, success is yours. If you wish to eat a cattail from the other end, peel back the layers until the interior parts are exposed and cook or eat raw. If you opt for developing flower spikes, they are best boiled and eaten like corn on the cob. If seed heads are present, you can place them in a bag and shake to release pollen, which can then be used as a flour to extend all sorts of recipes. Just be mindful of pollen allergies and take care in handling the fluffy section of a cattail as some people are prone to allergic reactions to it.
If you are interested in consuming cattails, being able to identify them successfully is key. Plants that are known to grow near and mimic cattails can actually be quite toxic, so remember that it must have a cattail to be a cattail. If the event that you find stalks that appear dead, a cattail may not be present, but you can pluck the stalk from the ground and look for the rhizome. If in the process you find a seedpod, the plant is not a cattail but likely a toxic iris which is not safe to consume. Without the rhizome, don't risk eating the plant and instead keep moving in search of something edible. Remember that cattails grow plentifully around the globe so the chances of stumbling across them are good, and when you do find some, a foraged meal is soon to be yours.