SAN FRANCISCO—Here's something you might not know about being a locavore, the new-fangled term for the old-school tradition of eating food grown close to home: Coffee is almost always negotiable. Here's another: The people practicing this new-old (and currently quite hot) trend may surprise you. Suburban moms? Check. Artisanal-cheese sniffing foodies? Double check. And how about denizens of the decidely un-hippie halls of Wal-Mart?