Kailua
The windward afternoon: lunch in Kailua town, then Kailua Beach or Lanikai's postcard sand and the Mokulua islands. Parking at Lanikai is tight — walk in from the loop road.
No booking, free. Park in the Kailua Beach Park lot (restrooms, showers, lifeguards) and walk or bike over to Lanikai — it has no lot, only narrow public-access paths off Mokulua Drive, and its street parking is limited and closely enforced, worst on weekends and holidays.