For being an island there is SO much to do and see! Living here my bucket list keeps getting longer instead of shorter!
Kaena Point is a great easy walking hike (hot though) and you can almost guarantee to see Monk Seals.
If you are going in winter try to do a whale watching tour most leave from the west side of the island
BRAND NEW zip line on the North Shore
http://www.climbworks.com/keana_farms
Kahuku Farm Tours
http://kahukufarms.com/ (great cafe!)
Arizona Memorial (you can just show up later in the day and get in the stand by line, no tickets needed, I have done this every time)
Punchbowl Memorial
Makapu'u Lighthouse Hike (fairly steep but uphill and even stroller friendly, beautiful views can even see whales in winter)
Hanauma Bay, don't even need to snorkel, just stop and take some beautiful photos from the top.
Halona Blowhole
Lanikai Beach (the stereotypical what you think of Hawaii Beach, Beautiful)
Kualoa Ranch (horse back riding, ATV's, movie tours)
Mac Nut Farm (great samples, amazing tour)
North Shore: Stand up paddleboard down the river (lots of turtles there), hit a shrimp truck (I prefer Macky's over Giovanni's) shave ice (it doesn't HAVE to be Matsumotos) Turtle Beach (Laniakea) is crazy right now, they blocked off all parking and it's a huge headache. Waimea Falls are another easy paved walk/hike through a beautiful garden and you can swim in a waterfall at the end (lifejackets provided, conditions permitting) They also have a great farmers market on Thursday afternoons. North shore waves are BIG in winter. Most beaches will NOT be swimmable. Highly recommend Ted's Bakery, great food and pie (Chocolate Mac Haupia is my fav) great to go and eat at the beach watching the big surf.
Dole Plantation is a quick stop, don't need to do the train, maze or anything. Check out the beautiful rainbow bark trees in the parking lot. Feed some koi, take pictures of all the cute pineapple growing, stick your head through a pineapple cutout and grab yourself a Dole Whip. Done.
There is a great little coffee stop just south of Dole, Green World Coffee Farm, stop in.
In Wahaiwa town there is a yummy chicken place, Maui Mike's.
If you can buy souvenirs from the Aloha Stadium Swap meet. Most of the stuff isn't made here so why pay WAY more for it. Great place to get beautiful sarongs, muumuus and Aloha Wear for those Luaus! Exceptions! If you want a REAL Hawaiian Quilt it is going to cost a LOT (knock offs made overseas will be dirt cheap) there are also some local woodworkers there that are handmaking tikis, really cool.
Any questions?