Urban foraging, gathering and trading

My interest peaked when I lived in the Bay Area - where the fruit trees are plentiful. Walking around Berkeley I could pick figs, plums, lemons, and avacados on my way to the BART station.
The house I shared had a huge plum tree from which anything imaginable from the fruit was made, including plum wine that was barely drinkable. A housemate's dog would pluck plums from the trees as snacks frequently. Then we discovered the neighbor down the street with the avocado tree in her backyard - apparently too many fruits to handle. What a great trade!
When I moved back to Richmond I met a guy and his zines. One of his local zines had a map of places to forage, harvest and gather. Mulberries, figs, blackberries, day old bread, discarded bruised fruit, and it went on and on. There is a certain joy in the happenstance of finding a tree bursting with fruit, right there next to the side walk, and picking until you've filled up every container and pocket. "Why isn't everyone else here, right now, picking these delicious berries?" Is it weird? Are they afraid? Do they just not know? I'm just not sure but I want to share it and encourage it. Start with a friend and you'll get hooked.

Here are some references to begin:
The Neighborhood Forager: A Guide for the Wild Food Gourmet by Robert Henderson
Stalking the Wild Asparagus by Euell Gibbons
Edible Wild Plants - Peterson Field Guide
The Uses of Wild Plants by Frank Tozer