My neighbor Jess writes a nice article that includes how to make pesto from nasturtiums. She's pretty keen on something she's calling "weed gardening." It's a technique of noticing what is growing really well in the margins of your yard, and using that as food. She made a successful quiche from sow thistle, for example.
I've been eating wild radish for as long as I can recall. I discovered it when I was perhaps 8, exploring the wilds of Orange County. I'd pull up the ubiquitous plant and chew on the thin bit of root meat surrounding the woody core, enjoying its horseradish like quality.
My yard right now has several hybrids of wild radish and other brassicas. The particular plant in the picture above is making giant, juicy, crisp, flavorful seeds pods. I'm munching on them nearly daily. Soon they'll start to set seed and they won't be so pleasant.
Have a look around your yard! See if there are any edible feral flora growing near you. Start simply, adding petals to salads and that sort of thing. Educate yourself so you don't accidentally eat something harmful, but by all means experiment and find what's yummy in your unexpected places!