It's too bad you aren't taking the LF gear. I can show you many thousands of images of this island, all taken with a small camera. LF there really stands out.
You've gotten several good suggestions, all worthwhile, all very standard tourist spots. I have three beach spots I like to shoot when over there:
There are a lot of good places to eat on the island; the best in my opinion is Keoki's Paradise at the Poipu Shopping Center - you may need reservations, this place is popular. I mentioned Bubba's, they have two stores - good place for a quick lunch. Also try Duke's and Kilohana Plantation. One more hint, for breakfast, the local favorite is the Loco Moco - rice, hamburger patty, brown gravy and eggs.
- Ke'e Beach, which is located on the North Shore (near Hanalei). This beach is fairly small and can get really crowded at certain times of day. But, if you hike just a little way up the Na Pali trail, there is a great overlook. There is a Heaiu (Hawaiian place of worship next to the beach, but I'm not sure if it is accessible to the public anymore. If you are adventurous, you can hike the Na Pali Trail to a secluded beach (the name escapes me at the moment) about 1 1/2 miles away, there is also a water fall not far from this beach. BTW, when in Hanalei, the place to eat is "Bubbas" - great hamburgers (they have a store in Kapaa as well).
- Poli Hali Beach, at the opposite end of the island, is a wide sandy beach, at the opposite end of the Na Pali coast. This beach has great views of the forbidden island of Niihau. You have to drive to the southern end of the road, and keep driving through some old sugar cane fields on a dirt road to get there, but it is well known.
- Kapaa. There is a small outcrop of rock just a bit north of Kapaa town, which I have found is great for sunrise shots. Although, this is a bit of a drive if you are staying in Poipu. If you are in Poipu, you can try Brennecke Beach.
BTW, there is usually an art show in Kapaa on the weekends. I know a couple of local photographers sell there, mostly digital/ink jet stuff, but it will give you some good ideas.
Feel free to ask me any specific questions you need.