If you like beaches, then you have chosen wisely.

I can give you the trip we did if you want by BM. Some highlights here:

Makalawena beach is terrific
Two or three other beaches on the Kona side are world class.
I would take a day and drive on the freeway that bisects the island over to the volcano/park. Then drive back on the south side of the island.
If you have kids, then chartering a boat for dolphin swimming is a blast and Captain Cooks is a must-do-activity for snorkelers. We did both on a small boat I rented for the day for our family.