You can drive to the top of Haleakala volcano (even if you don't do it to see the sunrise).
The is the Aquarium/oceanagraphic center to visit. There is a commercial site mid island caled the Plantation. There are gardens and atram ride through the plantation where thereis just about every native crop and plant. You can ride up to the Iao Valley . The view is fabulous and you don't have to walk up the path to appreciate it.
When are you going? December to March you can ride along the coast and find spots to see whales. There is shopping and galleries and historical sites in Lahaina.
Try a Luau. Old Lahaina Luau is reputedly the best. Shop at Whalers Village, and visit Hilo Haties near Lahaina. Go to the beach. There are many good ones, Kanipali is one of the nicest. Road to Hana is a good 3 hours each way , at least. Truly that will take the better part of one of your days.