Almost every car park on this coast is free and almost all of them are too small. That is the whole story.
Waimea Bay Beach Park has the one proper lot on the Seven Mile Miracle, with lifeguards and restrooms. It fills before ten in summer and earlier on a big winter swell. When it is full, cars spill onto the highway shoulder, which is both a ticketing risk and the reason the queue through the bay exists.
Laniākea has no formal lot at all, only a dirt pull-off on the mountain side of a fast two-lane road, from which people cross on foot to reach the turtles. If the pull-off is full, keep driving.
Ehukai Beach Park, for Pipeline, has a modest lot behind the beach that is gone by mid-morning through the surf season. Sunset Beach has a lot plus roadside space that empties and fills in waves as surfers come and go, so it is worth a second pass.
Shark's Cove parks across the road from the reef, with restrooms, sharing the lot with the food trucks. In summer it is the busiest small lot on the coast.
Haleʻiwa town has small lots behind the shops and a larger one at the harbour end. Park once and walk; it is a few hundred yards end to end.
The ticketed places — Waimea Valley, the Polynesian Cultural Center, Dole Plantation, Kualoa Ranch — all include parking, which makes them the easy days. Turtle Bay marks public beach-access stalls, because every beach in Hawaiʻi is public; there are not many and they go early.
One rule everywhere: leave nothing visible in the car. Break-ins at beach lots and trailheads are a known problem here, and moving a bag to the boot in the car park is not hiding it.