You can choose to rent a car directly, which will cost more than 3 dollars if you don't buy insurance, and then drive around the island, or you can just go to Wikiki Beach. The water is clear, the waves are not big, and you can even snorkel. Either drive directly to Pearl Harbor, visit it, or visit their palace.

If you don't want to rent a car, just take a taxi or a bus to visit Wikiki Beach or Pearl Harbor. After all, it takes time to go through customs.

there is no mailbox at the airport. I just looked around the day before yesterday and didn't see it.