Every August, millions of families make the Costco run before college move-in. The cart fills with twin XL sheets, noise-canceling headphones, snack packs, laundry detergent, protein bars, and the complete institutional supply of toiletries that will sustain a semester of dormitory living. The parking lot fills with sedans and SUVs loaded to the roof with the physical evidence of a child leaving home. For the parents leading this expedition, Costco is the obvious choice. For