Maui is beautiful but when you get tired of just relaxing there are plenty of activiites to enjoy.
On Maui (and all of the islands) you need a car to get around. Kapalua Resort has a wonderful shuttle service available at most hours which will take you anywhere in Kapalua Resort and is a free service to all those visiting the resort.
Being on an island your first thoughts might be to enjoy some of the water activities. All beaches in Hawaii are public and have public access. Enjoy a variety of beaches from the very calm to those where surfing and bogie boarding can be a challenge. For some of the motorized water based activities head down to Kaanapali where you will find sailing, snorkling and whale watching (in season) cruises. You can also enjoy some time para-sailing or renting jet skies (except during whale season). You might even take a submarine ride for an upclose view of the underwater world.
Hiking in the West Maui mountains or down into Haleakala crater can be a wonderful experience. There are a variety of guided and unescorted trips available. If you head up-country be sure to take a sweater and slacks as it can get cool.
A trip to Haleakala is a scene you won't soon forget. Sunrise can be beyond description, but it does mean getting up really early. Don't forget your jacket as it will be cold at 10,000 feet early in the day.
If you have the time a trip to the south end of the island is a great way to spend a day. Stop and see the variety of hotels and be sure not to miss the Grand Wailea Hotel. See their wedding chapel and visit the wonderful pool and beach areas. Likewise be sure to drive all the way past Makena and see the lava flows at the south end. You will know when you get there as you will run out of road.
There is lots of shopping for those in the mood. The old whaling town of Lahania is full of great shops with a wide range of goods to buy. Don't miss all the art galleries as Lahania has one of the worlds finest collections. World famous as well as local artists are featured and on Friday nights you will find that many of the galleries host an artist. There is a new shopping center in Wailea and Whalers Village in Kaanapali has a good selection of shops. If you are looking for golf related items check out the two pro shops at the Kapalua Resort courses. The merchandise is different at both and they have the full range of accessories.
The trip to Hana is often talked about, but we think it is overrated, especially if you are prone to motion sickness. We actually think a drive to Makawa (up-country) is a better idea and the views on a clear day can be breathtaking.
Don't forget that travel to the other islands is easy. Pearl Harbor may sound touristy, but everyone should do it at least once. The Volcano National Park on the big island is like nothing you have ever seen and Waimea Canyon on Kauai is as beautiful as any natural setting in the world.