Lots of great things mentioned above...
Maui on the Cheap (less expensive)
After walking and touring Lahaina, perhaps even taking the self-guided history tour of Lahaina get thee to the bus. (perhaps download the free Maui Bus App) The bus starts at the back of the Wharf Cinema building. Jump on the bus (Ka’anapali Islander or West Maui Islander) for a cheap cheap price and head to Whaler’s Village. This is the location of Ka’anapali Beach, Whaler’s museum. If you snorkel grab a cheap snorkel kit (leave it near the beach when done) at the ABC Store and head north of Black Rock for some beach and snorkel time. Or explore the area and get lunch at Hula Grill or Duke’s or one of the other restaurants.
Bus all day pass is $4 (ask the driver) or $ 2 a ride and $ 1 seniors
Or get on the Lahaina Islander and head toward Kahului and the Queen’s Mall but either get off at the Maui Ocean Center (Aquarium and other ocean related things here) this is a small mall. Or stay on the bus for another ten minutes and get off near the Maui Tropical Plantation. (Tell the driver as you won’t know when to pull the cord) Walk carefully down to the area and take the tour or just walk around. Do the Zip-line, if you are into that.
Haven’t got enough of the ship’s magician on this cruise? When in Lahaina go to Warren and Annabelle’s show. Skip the dinner, just get show tickets. Even the jaded always seem to like the show.
Of course, a luau would be nice, but you probably can’t get tickets…
You can check out all these things online prior to going… Plenty of you tube videos to watch
You could also go on a sunset dinner cruise out of Lahaina.