Originally Posted by lazycash

Uh, they are going to Oahu, not Kauai.

Here's a few things to do, I was just there two weeks ago.

Snorkel at Hanauma Bay
Hike Diamondhead
Have lunch at Dukes and dinner at The Shorebird (Both on Waikiki beach)
Go to the Mai Tai Bar (Waikiki - Royal Hawaiian Hotel i think)
Spend a day and drive to the north shore, lots of places to pull off with nice beaches and no crowds.
Go horseback riding and atv at Kualoa Ranch, beautiful place near the north shore where they filmed Jurassic Park.
Check out one of the many activities boothes if you want to parasail, jet ski, hike, kayak, dinner cruise or luau