For lunch in her modest apartment, Madeline Nelson tossed a salad made with shaved carrots and lettuce she dug out of a Whole Foods dumpster. She flavored the dressing with miso powder she found in a trash bag on a curb in Chinatown. She baked bread made with yeast plucked from the garbage of a Middle Eastern grocery. Nelson, 51, is a former corporate executive who can afford to dine at upscale restaurants. But she prefers turning garbage into gourmet meals without spending a cent. On this afternoon, she thawed a slab of pate that she found three days before...