There is just a ton of things to do in Maui. It's just a matter of personal preference. You can book ANY activity you want in Old town Lahaina. I can never get enough of that place. There is shopping, eating, drinking, art galleries, and historical sites. You name it. I also love the little surfer town of Paia, it's on the way to Hana, which is one of the most popular drives in Maui. It's a long but beautiful drive, just start out early.
Best Way To Get Around: Best way to get around is to rent a car or if you like a motorcycle. Depending on where you stay, some things are spread out pretty far, to far for a taxi.