About five years ago, I mentioned on this site that we like to pick and eat dandelion greens from our yard. This is an example of foraging: picking and eating wild food, where "wild" means anything that hasn't been planted on purpose. Brian and I aren't exactly habitual foragers; our scavenging is generally limited to weeds from our own yard, plus the occasional berry that we can pick while out walking. When it comes to supplying our own food, we rely much more on plants that we've actually planted and watered and weeded.
Nonetheless, I think foraging is an interesting and definitely ecofrugal idea. It's not merely getting food for free; it's getting food that was grown locally (in your own neighborhood) and organically (with no fertilizers or chemicals of any kind), without even using any water beyond what it gets from the sky. The carbon footprint of those dandelion greens we put in our salad wasn't just small, it was probably negative, since they actually absorbed carbon while they were growing.
But foraging also, quite clearly, has its risks. The most obvious one is eating something that could kill you, or at least strongly disagree with you. But it also has legal risks, since you can get arrested for picking someone else's plants without permission, and moral hazards, since you could inadvertently damage the environment by picking too much of a plant that's crucial to the ecosystem. And even if you don't harm the environment, there's still the question of how much you can reasonably take and how much you're morally obligated to leave behind for others.
In my latest Money Crashers article, I explore all these different aspects of foraging. I discuss the benefits of gathering your own food, along with the risks; I provide details about some common foods that grow in the wild; I discuss some basic rules for foraging safely and ethically; and then, since I can't possibly tell you everything you need to know in one article, I conclude by providing links to other sites and resources where you can learn more. But I hope that my article serves, as least, as a good, broad introduction to the subject, one that will whet your appetite for more information about the delicious and cheap bounty of nature.
Ultimate Foraging Guide – Edible Wild Plants & Food, Benefits & Dangers