Co-chaired by Derek Lam and Olivia Palermo, Fashion for Action combines designer ready-to-wear and charity into a four-day event. A ticketed benefit and silent auction are set for Thursday at the Rubin Museum, only to be followed by a free, weekend-long sample sale at the Chelsea Thrift Shop that features 150-plus high-end brands at half off (and more), including Acne, Band of Outsiders, DVF, Paul Smith, YSL, and a bounty of merchandise from the Gilt Groupe. Raising funds for Housing Works and its crusade to assist New Yorkers with HIV and AIDS, shoppers have an easy motive to buy-buy-buy: to contribute to the well-being of your fellows.