Pearl Harbor memorial is very moving, you cannot bring just about anything with you though... no pocket knives etc.
There is a tourist attraction on the north end of the island of Oahu whose name escapes me at the moment, but it is a series of villages that show all the various south pacific islander cultures. Quite interesting, just don't get dehydrated and eat McDonalds before you go in... I did and felt like puking the whole time.
Bring/buy a good hat and wear it... you don't want to sunburn the top of your head. It will make your trip much less pleasant.
Visit the island of Kauaii (sp?) if you can... very laid back and beautiful. Waiamaia canyon, Nepali coastline, good golfing, take the helicopter ride if you can.