There is a good number of restaurants, rice & curry shops and noodle shops in Phang-nga town. Thai Muslim food shops are also available. Besides, it is easy to find restaurants and food stalls in tourist districts like Thai Muang and Takua Pa, where Khao Lak and Bang Sak are located.
If you love seafood, go to the beach areas and you'll find that it is not only fresh but also delicious and cheap.