I was there about a year ago, but unfortunately I can't comment on the restaurants there. I was only there a day and self catered. I was staying near Oneroa, so I walked to a market there to pick up some food. The fresh produce looked nice (I picked up some yummy kiwi fruit) but the rest of the stuff on the shelves was pretty lacking. The market was pretty tiny. I don't know if there's anything larger on the island, I think Oneroa is the largest town. Waiheke was absolutely beautiful. I plan on going back in a few years. Enjoy yourself!