This is a grassy area right in front of the scenic overlook up on Tantalus (above Honolulu). The picnic is a very short part of the movie, but the location is great for seeing much of the south side of the island of Oahu.
This is the start of the opening scene with Maile driving down Round Top Drive, overlooking the Manoa Valley. Her route continues southeast for a short distance.
Ala Moana Beach Park is just outside Waikiki. In this scene, Maile is going to be stopped by a policeman. She turns left, off Ala Moana Blvd, into the park and actually stops a very short distance further on, in the park.
Hanauma Bay is a popular snorkeling area because of the reef in this collapsed volcano cone. In the movie, it shows Chad driving in from the southerly end, which is actually opposite the real entrance to the bay.
This is right by Sea Life Park. The scenes showing Chad and Maile driving to the beach house are not in geographically correct order as this location is just past the site they eventually end up (Hanauma Bay). In the scene, you can see the offshore islands.