Tim, you should take a day or 2 to get over to the West side of Kauai and hike the Grand Canyon of the Pacific Rim...Waimea Canyon State Park up RT 550 out of Waimea town. Don't miss the 'feel' of Waimea it's like going back to 1950, especially the movie theather! There's a grocery store and a few resturants here for resupply too. You can catch a bus from the shopping center near the airport to get to here, then walk, hitchhike up to WC with some luck.
When hiking Waimea Canyon be aware that the red rock/dirt you see here is very high in iron, and WILL stain any clothing or gear it comes in contact with! You'll see the famous red dirt shirts for sale in town....make your own with a favorite tee shirt= just get it soaked with water, then rub it all over with some red dirt, Presto! Instant souviner!
If you don't own a Montbell, GoLite or similiar light umbrella BUY ONE! It rains alot here and you'll appreciate having it tto walk in the open in the Sun. Lots of trails to hike in WC. Some muddy trails so wear gear you can ruin.
That's one day or two if you get a camping permit out at WC. a good way to start your trip is to start at one end of the island and work your way towards the other in order to see as much as possible. Hanapepe town has mostly touristy stuff and a few resturants.
Cruise the bus around to Hanalei and get off here to chow at Bubba Burgers, and walk back over the steel span bridge to the little fruit stand by the side of the road for some great local knowledge from the guy who runs it with his son and daughter.
You can walk out of Hanalei and find some hiking trails both Ocean side and land side, just respect property boundaries. Hanalei Bay was where I had the good fortune to actually see a whale give birth, and she then hung around for a week.
Do not attempt to go hiking in the Anahola Mountain area because this is considered VERY sacred by Hawaiian Natives and they do not like non Hawaiians hiking in this area.
Back down towards Lihue you'll reach Kapa'a, lots of resupply, eating, stuff to see, one of the few traffic lights on the whole island! Very congested, but you can get the bus here regularly. Not a good place to try and hangout over night due to the city atmosphere, unless you get a room.
The backcountry on Kauai can be brutal, wet, slippery, dense undergrowth, vertical lava ridges, no place to pitch a tent. Be prepared to hike back out same day if you find no water, or the trail gets lost. Since most places you won't have anyone to file a trip report with, no one will miss you if you lose the trail. This is especially important in areas where it's very wet as hypothermia can catch you unawares.
At the airport just walk out to Ahukini Road/570 and walk due North until you reach rt 56 on your left is a shopping mall you can get tthe Bus at. Enjoy your trekking.