Article has a bunch of details about the often amazing workings of Wal-Mart.
Another of Walmart's recent extra-commercial activities underscores its capacity and growing ambition. In the aftermath of Hurricane Katrina, the retailer mobilized its logistics expertise to facilitate relief efforts in the Gulf Coast region. Even before the storm made landfall, the company had anticipated supply shortages and had trailers loaded and ready in their Brookhaven, Mississippi, distribution center. Right after the storm, Walmart dispatched trucks stocked with supplies to affected areas in Louisiana and Mississippi — often ahead of the National Guard. As one local church official noted, "If the American government would have responded like Walmart has responded, we wouldn't be in this crisis."  Since then, and with its logistics network as a model, the retailer has built nine "Disaster Distribution Centers," and stocked them with relief supplies and processing equipment in preparation for future calamities. 
Link via Conor Friedersdorf's "Nearly 100 Fantastic Pieces of Journalism".