Morning snorkeling at Kealakekua Bay, afternoon exploring Kailua-Kona town and Kona coffee farms, evening manta ray night snorkel.
Full day at Hawaii Volcanoes National Park — crater overlooks, Thurston Lava Tube, Devastation Trail, and (activity permitting) an evening glow viewing.
Downtown Hilo and farmers market, Rainbow Falls, then the scenic Hamakua drive to Akaka Falls and the Waipio Valley lookout.
Relaxed morning, afternoon drive up to Waimea, sunset and stargazing at the Mauna Kea Visitor Information Station.
Drive to Ka Lae, hike or shuttle to Papakolea Green Sand Beach, and stop at Punalu'u Black Sand Beach for turtles on the way back.