As I mentioned before, Kihei through Wailea have lots of hidden little beaches. We were staying accross from one, Keawakapu beach. There is public access, with gravel parking lot. Nice clean little beach, some acreage for walking around too. Even better, there is a bar right up to the beach (part of this hotel/condo units). The Five Palms Beach GRill. Nice bar, TVs, etc. open air, can see the beach...have a drink and wander back to the beach to take a nap.
Kihei Car Rentals, Behind Marco's Restaurant, close to Lipoa Street, Kihei Maui. Just call them up or drop in, they are very helpful! They also have reasonable rates for van rides to/from the airport. Here is the jeep I rented. We could not find mopeds to rent, or the mopeds were more expensive than the jeep, so we rented this cool jeep, and went north to Kite Beach, and cruized all around the island!
Go to La Perouse bay in the morning for snorkeling. Take nothing of value because you have to leave your car in an isolated area (you don't need 4WD). Best place to snorkel without having to pay someone.
Haleakala is just over 10,000 feet high - and beautiful. You have to park your car and walk the last little part, but it is not difficult. It can get cold up there, so take a jacket!