There are many useful plants around us. The pastures and parks are full of them. A group is working on compiling a 12-volume encyclopedia of the ones found in Texas and I can't wait for them to get it done! They need help, so if this interests you, please go to the site and see how you can volunteer. They need people to do a wide variety of things ~ growing plants for sale to benefit the project, giving talks about useful wild plants, photographing useful wild plant events, even proofreading articles.
On this same note, DragonFlyWings told of how milkweed pods are edible and asked about other edible wild plants on this thread, and I answered:
I didn't know about the milkweed pods, Dragonfly! Cool! I've made jelly from those hog plums, as well as the wild grapes, prickly pear cactuses, dewberries and agarita bushes (a good trick to harvest those is spread a sheet out below the bush and use two sticks to harvest ~ pull one branch out with one stick and tap that one firmly with the other stick ~ all the ripe berries will drop onto the sheet). There are also wild persimmons ~ not the little black things, but real persimmons, yellowey-orange and everything. They don't taste very good if we don't get much rain, and still don't taste nice until after a frost. Well, they still don't taste really good unless you add a lot of sugar. LOL! And of course who could forget pecans. I make pies and pies and more pies every year from those, as well as add them to soups, salads and stir-fries.
Speaking of salads, there are wild onions, pickle plants (those light green "shamrock" sort of weeds ~ you eat the seed pods), purslane, watercress and sorrel to flesh out that salad of dandelions. And wild mint to go in your tea or mint juleps. And chicory for use as a coffee substitute. If you want a cooked dish, use those sorrel leaves with some lambs' quarters and spiderwort to add to soups and such like spinach. And you can cook young prickly pear pads after burning off all the spines. They're good in scrambled eggs and are called napolitos in Mexico. They're even sold in cans in HEB.
As for medicinals, there is mullein for chest congestion, senna for constipation, the aforementioned horehound for colds (IF you can get past the naaaasty bitterness), and tickle tongue tree (aka toothache tree) to stand in for Oragel (it really does make your mouth numb).
Euell Gibbons is a great resource! He wrote two or three books, but the most popular was the first one Dorothy mentioned. Another good book for our area is Edible and Useful Wild Plants of Texas and the Southwest by Delena Tull. I can't personally attest to it's usefulness yet since I just bought it (just a minute ago took the plastic off as a matter of fact), but three people have told me that it's a really good one. This thread's got me motivated to read through it this morning to see what it says about the things I've already been using (the things listed above). The cover says it contains recipes as well as information on natural dyes, harmful plants and textile fibers.