Sky Diving, just about 30 minutes north at Sky Dive Hawaii, (
http://www.skydivehawaii.com/ )
Surf, surf lessons at several paces along north shore (
http://northshoresurfgirls.com/ )
Luau at Cultural Center (
http://www.polynesia.com/ ), and be sure to go there early, take tour, stay and pay extra for the show after the luau.
Snorkling along North Shore (
http://www.hawaiisnorkelingguide.com/sharks_cove.html ).
Honolulu is the main town on Oahu, lots of clubs and tourist entertainment in the Waikiki district, but the main recreational (and away from family crowds) is up north about 30 minutes.