H.P.
We did a 15 night cruise out of LA to Hawaii, going to these ports, though the Kauai port was canceled, so we spent 2 days in Maui. On the big island, it is a must that you go to the Volcano Park. It's awesome! If you have never been to Pearl Harbor on Oahu, it's worth the visit. Hanama Bay is also fun to go to, as is the International Market. Don't miss Waikiki Beach though. In Maui, you can bike ride down Haleakla, snorkel Molokini Crater(awesome), go to the Maui Ocean Center, or just hang out in Lahaina. They also have the train excursion(the Lahaina Kaanapali Railroad) which is fun. On Kauai, my parents liked the grand canyon of the pacific, though I know several people that have taken the Zodiac boats to the Na Pali coast for snorkeling. That is what I was supposed to do there before that port got cancelled. That is supposed to be one of the best snorkel adventures in Hawaii, so book EARLY as it sells out quickly.
Aloha!
H.