Betty is feeling a bit unloved and so drives off to a beach. It's an impressive feat when you consider the beach is actually on Lantau Island and not easily accessed by car in the mid-70's.
The more eagle-eyed HK film fans out there may recognise this place from another film - albeit one made 30 years later. You can see this beach at the beginning and end of SPL: Sha Po Lang starring Sammo Hung, Simon Yam and Donnie Yen. Dan's location blog has a post about it here.