Aloha,
Check with the Waikiki Aquarium and see about the night time tour, it changes your perspective of the place you see in the day time.
If you are headed to Hanauma Bay, go early because they started limiting the numbers of folks in the park. This policy went into effect in the late 90's and was still enforced when I was there in Sept 03.
If you are stuck in Waikiki then drop in for Dinner at Irifune on Kapahulu for great Japanese food with an Island flare and don't miss breakfasts at Egg-n-Things on Kalakaua Ave and McCully St.
Aloha.
btw:Don't leave out Molokai if you are island hopping It is the affordable getaway and has the Molokai Express for a great "drop in here, get picked up way over there" wall dive.