Filling out a daily schedule is not a tough task on Kauai (or any of the Islands): Find a beach to snorkel and hang out, find a trail into a tropical forest, and seek to soak in some Hawaiian culture. Hideaways Beach (above) in Princeville is a good place to punch the snorkel ticket.
The Powerline Trail (above) that extends from above Kapa'a to the North Shore is a spectacular hike that sees little use, given other trails in the vicinity. Hiking the whole trans-island route is a challenge, since it is overgrown in the middle. A better choice is to do an out-and-back from either of the trailheads.
You really can't set foot anywhere in Hawaii without being immersed in cultural traditions. A family favorite is the Smith's paddleboat tour up the Wailua River to Fern Grotto. The Smith family has operated the boats—as well as a tropical garden and luau—for more than 60 years. Kayaking is also a popular way to see the wide Wailua.
Trailblazer Travel Books provide an inexhaustible menu of triple-play-day options for all the Islands.