most of us are on Oahu, at least Maui still has a track, they took ours away. take Hana road in a convertible if you can. You will have scenery overload. Aloha
The Hana road is absolutely amazing. Just don't get in a hurry. It is a narrow, twisty road with countless blind curves. Watch out for the crazy locals. But, you will be rewarded with some of the best scenery you can imagine. Plan on taking a whole day for the trip. Go a little past Hana and you'll come to an old church/graveyard. Charles Lindbergh is buried there.
Take a bicycle ride down Mount Haleakala, but be sure to take a coat. At 10000+ feet it gets cold. You don't do any pedaling on the way down. Gravity works well.
If you're scuba certified, go diving at the Molokini crater, but do that before going to Haleakala.
If I could make a living selling painted coconuts to tourists, I'd move there in a heartbeat.