Every fall, finding classic rock is as easy as crossing a bridge to Gretna. In recent years, the Gretna Heritage Festival has featured such where-are-they-now acts as Eddie Money, Foghat and Three Dog Night. This weekend (Oct. 2-4), Chicago, Kool & the Gang and The Guess Who headline. The rest of the lineup stretches from Allen Toussaint to Dash Rip Rock. Visit the Web site (www.gretnafest.com) for complete details.