I did the following a few years ago (listed in order of enjoyment):
1. Molikai Mule Ride..part of the tour is a short flight to Molikai..it was expensive but a great tour...
Tour: The Kalaupapa National Historical Park and Guided Mule Tour
2. Sunrise bike ride down Haleakala volcano... you got to get there before dawn and it is actually cold up there then. The bike ride was over 30 miles and all downhill.
3. Scuba at Molokini Crater and "turtle town".
4. Day catamaran sail to Lanai...saw dozens and dozens of spinner dolphins
5. Road to Hana...bought a tape at a gas station close to the start that had a narration of the entire trip. (i.e it tells where to stop and what to look at, etc. as you drive along
6. Did a luau in the Lahaina area....In my opinion they are kind of a tourist rip off.
I bought the tours through a "time share" company to get a very good discount. I did save about $200. The bad news was that I had to sit through a time share presentation (about 2 hours). :(
You should wait and go after football season to see the whales: Hawaii?s whale watching season takes place from late November to mid-April.
Aloha-Hawaii.com: Whale Watching in Hawaii