When we did the drive to Hana, some friendly fellow had left a narrative tape in the car that points out sights along the way - I can still hear him say "turn me off now and turn me on again, when you pass the mile 13 marker..." - This may be worthwhile, because you get the background story of the road as well as pointers to some sights that are a couple of hundred yards from the road in the forest - you might have missed them otherwise...

Do: Snorkeling in Turteltown, skip Molokini, it's crowded and the water quality isn't very good, I enjoyed Turteltown much more. The catamarans leave early, but it is worth the trip. Rent your own snorkeling gear, if you plan on using it for a while. We went to Snorkel Bob's in Lahaina and for me (short-sighted) having a prescription strength mask made it a wonderful experience.