Peapod is turning delivery trucks into virtual supermarkets, adding billboards that shoppers can scan to make purchases. The trucks, with a rotating roster of 23 products, will travel to summer venues along the East Coast, including concerts and baseball games. "When we piloted the virtual stores last fall, we found that the advertising stopped people -- it engaged them, and we saw mobile-app downloads as a result," Chief Operating Officer Mike Brennan said of a similar campaign at bus and train stations. "This go-round, we're exploring new, hyperlocal platforms to communicate our convenience message of 'Shop anywhere, anytime with Peapod.' "