just carts and bicycles I think. If you are staying close to SP, you wouldn't need one everyday. I think folks staying at resorts further south might rent carts or bikes by the week, because it would be one hot walk. I saw people walking from Mar de Tumbo beach area though. Lots of them. a cart is plenty fast enough. Depends alot on where you are staying, and if you mind walking.
You can walk everywhere but on the north end and far south end. And, with a bike you can go everywhere, too. I saw scooters but that was the exception and when on AC you don't spend too much time on land anyway!