When we stopped in Kahalui in Maui, we rented a car and drove around to explore the island. We reserved a rental car, but there were folks who took the chance for available cars. There were car rental shuttles to take you to the airport and back. In Lahaina, we took the public bus to the resort area to hit the beach. In Kauai, a trip to Waimea Canyon is your best bet. We did a ship's excursion, so I don't know how to arrange a private drive to the canyon. We did ship excursions in both Hilo and Kona. In Hilo we went to Volcanoes National Park. We did see a lot of cruise ship passengers in rental cars, so it shouldn't be too hard to do. Kona has a small beach near the tender pier, and it is a lovely town to walk around - which we did before our snorkling excursion left. All islands were lovely. You should enjoy your cruise and your vacation.