You would be surprised. Dandelion for example is a plant that thrives in cities, is entirely edible, and you can roast it's taproot into a delicious coffee substitute.
I started out with dandelion actually. I made a whole plant tea out of it heat dried. It entirely transformed the plant into something that smelled delicious, almost this floral toasted honey smell.
Just don't take from places where a lot of pets get walked, right next to roads, or sprayed. Wash everything and anything you take home throughly, and research research research before you start picking.

