Helicopter tour around the island
Captain Andy's catamaran trip up the Napali coast (pick the BBQ option over the build your own sandwich)
Horseback adventure to a waterfall with Princeville Ranch Adventure
Kayak up the Hanalei river
Get a massage on the beach (there are location for this on the north, east and south side)
Take a surf lesson. Learning how to surf by the pier in Hanalei bay is probably the best place in the world to do it.

Hike as much of the Napali coast as you can (first two miles to the beach, another two to the waterfall, or all the way)
Hang out at Hanalei bay! Jump off the pier (technically illegal), surf, paddle board, swim, and lay on the sand
Tunnels beach do everything here.
Best places to watch the sunset are Poipu beach, Polihale, Hanalei pier, and Ke'e beach
Best places to paddle board for beginners are the Hanalei river, Kalihiwai river, or Wailua river
Best places to snorkel are Poipu beach, Ke'e beach, Anini beach, and Tunnels
Best rock to jump off of is at Shipwreck's beach in front of the Grand Hyatt
Best beaches to body surf or bogie board at are Kealia beach, Brennecke's, Hanalei bay (time of year will vary some)

Dinner at Merriman's Fish House at Kukui'ula in Poipu
Breakfast at the Makana Terrace in the St Regis (best views in the Hawaiian Islands)
Pho Kapaa
Kilauea Fist Market
Eating House 1849 at Kukui'ula in Poipu
Happy talk in the Hanalei Bay Resort in Princeville
Lava Lava Beach Club (beach front dinning where you can literally put your feet in the sand) in Kapaa
North Shore General Store (breakfast sandwiches and lunch) best food you'll ever have from a gas station
Puka Dog in Poipu
Uncles of JoJo's shave ice
Pink's ice cream in Hanalei (you might see a celebrity while you're there)

What Are The Best Things To Do On Kauai? Here Are A Few Top 10 Lists For You!