I went to Oahu about 7 years ago YIKES!! Feels like yesterday sometimes! You gotta do a lu'au (obviously) and I would hike Diamond head (hike to the top, its fun) and then the other obvious is to go to Pearl Harbor. Other than that... we rode one of those ocean bikes, that was kind of cool and we went out to the Dole Plantation and you could learn to surf in the Bonsai Pipeline (best surfing in the world) ... and snorkling at Hanuma Bay! We also did a catamaran dinner cruise which was a BLAST with polynesian dancing! And we went to some reservation where you pick 2 activities from like horse riding, kayaking, atving, etc... and you get an hour with each activity and there are natives doing dances and making things like pots and crowns from tree leaves, there is also amazing cliff diving shows... it was really cool!!! Oh and the marketplace! You gotta go to the marketplace! And see Christian Larson's studio.. hes an artist out there and his work is beautiful!! We also went to some dinner/magic show that was very entertaining! I can't remember the guys name though (this WAS almost 7 years ago, he might not be there anymore)
there are NO turtle's in turtle bay! haha We were driving around the island and saw a sign for turtle bay so we went to it and were disappointed that not only could you not swim, but there were no turtles!
Hope I helped!!! I loved it out there... I felt sooo at home!