In the Cub parking lot, Mark, the attendant on duty, rounds up a long snake of carts, adds a dozen from Qasim's latest load, and winds the whole bunch into the store's side door. Meanwhile, a steady stream of loaded carts pours from the portals of Midway's megastores. Some head for cars in the parking lot, others for the bus stops. Some wobble through the slush out into the neighborhood. It's no Lincoln Navigator, but the shopping cart may be the most popular utility vehicle in the country.