For bargains, shop thrift stores in ritzy zip codes—or vintage stores in less cosmopolitan cities, where things might be less picked over. Call ahead for store policy; if it's a buy/sell/trade store, bring in your own castoffs for cash or store credit. Shopping online can also be worth the time, since prices there are often 40 to 50 percent less than in high-end boutiques.

Liv Tyler brightened up the city sidewalk in a vintage dress from pal Helena Christensen's N.Y.C. shop, Butik. "I often pop in on afternoons off," Tyler has said of the spot.