Eat, walk around seeing the sights, shop. At some point walk across the bridge to Kittery foreside for more eating. Make sure to walk around prescott park and strawberry banke. Not sure if the docks are still open, but if so, try to get a table at one of the waterfront restaurants. Maybe take a boat tour around the piscataqua, there's one that goes up-river for foliage, but there's a couple others.