To Kirsten Brydum, a passionate 25-year-old community activist from San Francisco, one person's junk was another's treasure. Brydum, who wanted to change the world, certainly changed Dolores Park. Because of her, there is something called the Really, Really Free Market. People bring their rummage to the park on the last Saturday of the month and give it away. Nobody gets any money and everyone walks away a little richer. That was how she liked it. -SNIP- In Manhattan, she spent a long time examining trash bins, marveling at the useable stuff that New Yorkers threw away. In St. Paul, Minn.,...