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Chamonix, France - 08/29/2013: Content of Timothy Olson's backpack for UTMB 2013. Most of the material is mandatory (like two pairs of headlamps, a drinking cup or a survival blanket), but every runner has some degree of freedom to customize his kit. Tim's bag is said to weight approx 4.4 pounds (2kg). Credit: Niels Ackermann for the New York Times