Kauai: Remember there is only 1 two lane Hwy from north to south. Down south you have Waimea Canyon. To do this properly is about a day. Take a picnic lunch. Drive to the top. Resist the turn outs. Drive as far as you can and then hike past the top parking a bit. There are several View Points up there. Have your picnic lunch in the Park at the top. Then stop at all or most of the View Points on your way down. There is the Kauai Coffee Planation. There is zip lining in Koloa. There is an inner tube float down the old sugar cane canals in Lihue. There is Poipu Beach. There is the Alakai Swamp Trail. There are Cruises out of Hanapepe Bay to the Napali Cliffs and snorkeling. There is the Spouting Horn. There is the Mala'ulepu Trail that starts on the top of the Cliffs just north of Shipwreck's Beach. There is the Makauwahi Cave. Almost forgot about the light house - a National Park. Also a bird nesting area. Luau: some of the large Hotels have Luau. The two I would recommend are Kilohana just outside of Lihue or Smith Family by Kapa'a. Kilohana has the more traditional entertainment telling the Polynesian story through song and dance. Smith Family has greater diversity to honor the many people that have emigrated to the Islands. Remember Poi is not a dish by itself but to dip your Pork. There is Anini Beach. The town of Hanalei. The beach at Hanalei. To go to Ke'e Beach you need to go online and make a Reservation - either AM or PM. Kayaking up the Wailua River to the Fern Grotto and Secret Falls. It is about a mile hike to the falls. Sometimes the trail is very muddy. In Lihue there is a Costco. Cheapest gas on the Island by a lot. Great Fish Tacos at the Food Truck by Hanalei Pier. Some of the best Chili Pepper Chicken is at the Chevron Station in Priceville. Best Loco Moco is at the Food Shack on the side of the Sueoka's Market in Koloa. Jump off the Cliff just north of Shipwreck Beach and swim to Shipwreck Beach.
If you have an upcoming trip to Kauai and plan on going to the North Shore, this thread on TripAdvisor's Kauai Travel Forum might be helpful. It's a long thread, but has regular updates on what's going on.
(See post below)
Visiting Haena State Park (by car, bike, on foot) now requires a pass, which you can buy up to two weeks in advance. There are only 100 parking spaces, so if you are driving, you need to reserve a spot for either 6:30am-12:30pm
through the end of the day. The afternoon permits sell out fast, so book early. People are reportedly buying more than one pass (one at a time). Parking permits are $5/car and include entry for all passengers. The park website is: https://dlnr.hawaii.gov/dsp/parks/kauai/haena-state-park
If you're not into walking or biking in, another other option is to buy a ticket for the hourly hop-on/hop-off shuttle bus @ $11/per person (includes the $1/pp park entry fee). The shuttle website is: https://kauainsshuttle.com/reservations
/ and https://kauainsshuttle.com/shuttlestops
/ It has just started, so how it will handle the flow of tourists will be interesting.
• A “no parking” zone has been established between Haena Place and Kee Beach. Parking along Kuhio Highway in this zone is a violation of Chapter 291C-111 of the Hawaii Revised Statutes and could result in fines of $200.
• Access to the Department of Land and Natural Resources’ Haena State Park is by reservation. More information is available at https://www.gohaena.com
• Information on the community-run Kauai North Shore Shuttle is available at https://www.hanaleiinitiative.org