Flip-flops are a summer staple—but now they can do much more than just keep your feet cool. FitFlops use patent-pending technology to challenge your leg muscles with each step. "So while you're walking, you're doing a little workout," Heidi says.

Available at Macy's, Bath and Body Works, Victoria's Secret and Bliss Spas; approximate value $49.99–$69.99; 800-BUY-MACY; thefitflop.com

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