Oahu does have public transportation just about anywhere but I wouldn't recommend it. Being on vacation and waiting for a bus is not something I'd want to do. I'd definitely opt for the car if it's in budget. The drive from your Waikiki Hotel is about 20 minutes to
Pearl Harbor, and about 30 minutes to Sea Life Park (Kudos on going there!...I love that place). So, having the freedom in leaving when you want is definitely a plus in Hawaii. Especially if you want to enjoy some of the nightlife.
A *must* stop would be
Hanauma Bay. It's only about a 30 min drive from Waikiki, and it's got some pretty popular snorkeling spots. As far as ATV Tours go, Destination360 has some great recommendations for
ATV TOURS. Destination360 also has some great details on
Snorkeling in Hawaii.
I know you said food wasn't that high on the list....but I would definitely recommend trying out some of the local foods. If you get the chance to venture off to the North Shore side try some "Shave Ice"....preferably Matsumoto Shave Ice. Many famous stars like Jason Scott Lee and Tom Hanks have been there. It's loved by locals and visitors.
Hope that helps...if you need more info, just ask.
