My family has stayed at Waiohai for the past five years.
We've done snorkel cruises on most of the islands, but Captain Andy's was the only one that gave us motion sickness (about 50% of the attendees got it also). They passed out "aloha buckets" at the start. Be forewarned...
For Helicopters, I'd recommend Safari. Great price. We've done it twice.
Tubing is a must-do, but it sells out a week in advance. Call ahead for your reservation; you can cancel up to 48 hours ahead.
Check out Spouting Horn (10 min drive)
Kauai ATV is nearby and if you get a rainy morning, you get a great mud run. It sells out quickly.
At the Shops at Kukuiula you can sign up for zipline. Leaves right from there. Very convenient. Not the best zipline I've done (that was on other side of the island), but it's good.
My favorite fish tacos are at Merriman's (downstairs), which is a 2 minute drive. Go during happy hour and save a few bucks.
Next to Merriman's is The Eating House 1849, owned by Roy Yamaguchi. Not as good as Roy's in my opinion, but still good food.
Also in that mall is Bubba's Burgers and Uncle's Shave Ice. Uncle's has the best shave ice near Waiohai.
Or if you want some incredible ice cream go to Lappert's in the same mall.
If you are staying in Waiohai the right time of the month, there is a Farmer's Market in this mall. Definitely go if it's there. What you want to get is the sugarloaf pineapple (white pineapple). It is incredibly sweet and even the core is tender enough to eat. You can also find it at the Living Foods market, near Merriman's. Be prepared to pay dearly for anything at Living Foods..
Get great poke at Koloa Fish Market, in old Koloa Town (7 minute drive). It's fresh - not previously frozen like the markets sell.
You can also get good pizza in Koloa Town at Pizzetta.
There is a little market right off the roundabout (Kukuiula Market) that sells the BEST burger meat. Bring it back for great burgers.
In that same market is a very good sushi bar (Makai Sushi). Small menu. Get a Gorilla Bowl and go to heaven.
Next to the little market is a tiny Mexican food place called Da Crack. Always a very long line.
The Beach House is the place to go for a good upscale meal with a view. (5 min drive)
You also have to get the obligatory Puka Dog in the Poipu shopping village (nearly across the street from Waiohai).
For a quick and good sandwich, stop by Brennecke's. They have a quick service next to the restaurant. Good prices.
When stocking up for the week, hard to beat Walmart (20 min drive, in Lihue). Costco is also out in Lihue.
Big Save is nearby in Koloa Town. The prices are higher than Walmart, but it's close.