The truth is that you need a week at least for each Hawaii island, and probably more with Maui, Hawaii's second largest island.
If you are visiting for a short time, I would recommend that you stay in a hotel with a little kitchen so you explore more and spend less. It is also a better option for vegetarians because veggie food options are slightly limited. That said, grocery stores carry pretty much anything you may need to cook simple, healthy meals.
On our last visit to Maui, we stayed in an area called Kaanapali, close to Lahaina. We did venture out to other places across the island but we also spent decent periods in those areas. Based on my time there, here are things I recommend to see / do.
There is more than one farm out there, some farms even sell pineapple ice cream! We went to Maui Pineapple Tour where we were driven around in a little bus around the Maui Gold Pineapple Fields, stopped to taste some pineapples and then also viewed the pineapple cleaning and packaging process. Pretty cool stuff!
(Insider Tip: Right next to this farm is a glass blowing shop, check it out!)
We like our alcohol SO MUCH BETTER when it is organic, so we had to go to the Hawaii Sea Spirits farm - especially since we had seen their Ocean Vodka product at Whole Foods.
They say its all about the story, and these folks have a good one. They use organic sugarcane (grown right here!) and deep ocean mineral water in their distillery. There was a nice show and tell, tasting and everyone had a good time.
A rare and sacred landscape is really the best way to describe this place. It is quite windy up there at 10,000 ft over the Pacific Ocean and parts of this massive volcano crater looks like you are on Mars. You can book a tour in advance to see the sunrise or you could just make your way up there in the early afternoon (like we did) to experience this landscape. It is an unforgettable experience.