Man, there seems to be a lot of stuff to do there. We are only going to be in Maui for 2 days and Honolulu for 2 days.
More or less man, I was there a full week and had to drive everywhere. The road to Hana you'll need to take a tour, the road is pretty nasty
This will sound weird...but try McDonald's for breakfast...portuguese sausage, eggs and rice. Righteous! Also...attend a real luau...where they actually cook the pig in the ground. Most resort hotels will offer these.
Ditto on the luau, if you do it on Maui do the one they do on the actual beach as opposed to the hotel one, cost more but worth it.
When i was a little kid, about 9 years old, i stayed at the waikiki hotel and went down to the beach everyday. Theres a huge banyon tree that is extremely fun to swing on. =]
Not to try and hijack all the good advise you're getting, but anyone out there have advice on Kauai? Heading there in February
The must do's are listed on this 1st page for each island. http://www.gohawaii.com/about_hawaii/learn/choose_an_island On Oahu, I also strongly suggest the Polynesian Cultural Center. http://www.gohawaii.com/listing?id=7679
Never been to Maui, but theres several cool places to eat in Oahu. For breakfast: Try Boots N Kimos - Their macadamia nut pancakes are great! Its a hole-in-a-wall kind of place where you have to order outside (because of the line) and theyll serve you once you get inside. Lunch: Any shrimp shack is good. Romy's, Fumis, Giovannis. Fresh shrimp, simple, good food. Dont forget to visit the shave ice to cool off. Someone suggested Matsomotos. Its huge. We ate in for dinner, but you can always try authentic Hawaiian food like in Helena's. Hope this helps!
My wife if from there...so we end up going about once a year...and will probably retire there. To see... -Na Pali coast tour -Drive up to Kokee/Waimea Canyon --- this is an absolute must. The scenery is beyond description. -secluded beach get-away - west-side - Polihale State Park -Spouting Horn Park (southside) - near Poipu -Koloa shopping -Tunnel of Trees - just east of Koloa -waterfalls - most famous - Wailua Falls -take charter over to Niihau (never done this but hear it's pretty neat) To eat... -Duane's Ono Char Burger - some of the best hamburgers I've had (I would put them up against In N Out and WhatABurger). -Hamura's Saimin Stand - my wife's family and the locals swear by this place. Very cozy local flavor. This place is a must...and don't be discourage when the ladies that work that display their complete lack of personality. I think the food will speak for itself. Definitely avoid driving on the eastern side of the island during rush hour. The Lihue - Kapaa stretch will back up severely and you might spend a few hours stuck in traffic. The cheapest gas is at the Lihue Costco. If you're not a member...borrow someone's card for the trip. Everything pretty much shuts down at 9pm.