In and around Kona help
i'd recommend Basik for a healthy breakfast or midday snack before a day of adventuring...
I'm really not into the whole acai bowl craze, but was taken here by a friend and these are damn good, made with nice ingredients. I recommend the Banyan Bowl...
Manta restaurant at Mauna Kea...beautiful setting, wonderful food. Go before sunset for a drink at Copper bar and wonderful hula.
Merriman's in Waimea is always a hit.
A must stop for us is at the Kohala Coffee Mill in Hawi for Tropical Dreams ice cream. Last time you could also buy it in one of the groceries in the Waikoloa resort and Foodland at Mauna Lani but selection was limited.
I havent been in Kona in a while, so I hesitate to reply - but maybe it will engender responses.
I would definitely check out Sam Choy's "new" place (Kai Lanai?) and I've always liked Huggo's. Da Poke Shack is also supposed to be quite good. Another one on my bucket list.
If you want to take a drive (well you did say you have a car) then probably a trip up to Waimea to Merrimans. I've only been for lunch, but it was enjoyable.
If you want to head the other direction, I've heard good things about both Rebel Kitchen and Manago Hotel Restaurant in Captain Cook. Sorry, no first hand experience.