Good point from Penny on the whale watching; you are more likely to see whales AND it will give you some time to walk around Lahaina, a charming (and touristy) little town with lots of shops and seaside restaurants.
I have done all your other excursions at various times and loved each of them. The best snorkeling I have ever done was in Kona.
And from reports I heard, I believe the luau on Kauai is much better than the evening one in Honolulu. Most people thought the evening one was too long and drawn out.
In Honolulu you will have time to strike out on your own when you return from your excursion, if you are so inclined. Waikiki Beach is an easy city bus ride or free shuttle ride away. We had Mai Tais at the oceanfront patio bar at the stately Royal Hawaiian Hotel, with Diamond Head in the background--how much more Hawaiian can you get?