When I went there I stayed at moana surf rider, best hotel, awesome breakfasts!!! Flew with Hawaiian airlines and they were really good, no problems at all besides the toilets being tiny as.
In may youd probably want to surf at Waikiki beach is pretty good and I had a few turtles swim past me.
You will definitely want to go shark diving but they only let you go in a cage, awesome experience, the water is a little chilli so take at least a rashie.
Hiring a mustang is well fairly expensive I cant remember how much but I think it was like 200 for the day or something.
Food there are a few good places cant remember their names but theyre on the main strip outside of my hotel.
Shopping is shit, its expensive and not worth the waste of money. There are hawaiian markets that were straight across from my hotel as well.
Scuba diving is nothing special over there most of the coral is brown/grey however if youre lucky you will see some of the biggest fucking turtles ever and they will swim right up next to you and you will realize how huge they really are, you will also see some okay fish and very rarely will you see sharks.
Depends where you are staying too, I was on waikiki beach I think the north shore is more resort type places instead of hotels etc. I didnt spend much time at the north shore.