As mentioned, Young Guns, Power Edge, and the Swap Meet will give you the best selections. If you go to the swap meet, remember the sun screen, water (they sell drinks/food there but it's really expensive), and good walking shoes (and probably a hat). If you like Japanese food (sushi, etc.) then there's a small Japanese restaurant across the street from Power Edge called Maguroya that I like to eat at when I'm in the area. There's also one a little higher up called Suzuki that's good too. The best parking for Power Edge (if you can't find street parking) is probably the small parking lot behind Maguroya, but all the parking around there is metered so bring quarters.
For food, there's lots of good places to eat. If you venture near Ward Warehouse (shopping center) there's an upscale "plate lunch" place called Kaka'ako Kitchen that's good. If you head down to the North Shore, then drive through Haleiwa (don't take the bypass) and there's some good places in there along with the aforementioned Matsumoto's Shave Ice and Aoki's Shave Ice is a few doors down--there will likely be a bit of a line at both but it's worth it. You can get your shave ice with ice cream in it or azuki beans (I don't like the beans but a lot of people do). I hear Haleiwa Joes is a good place to eat as well. North Shore also has Waimea Falls Park (I think they're still open) and then if you drive a lot farther down you'll get to Polynesian Cultural Center like JCM298 mentioned. Where are you guys going to stay? I like to walk around the Hilton Hawaiian Village when I can. There's flamingos and other birds walking around the grounds as well as a small penguin habitat, which is pretty cool. I think they also have live music at night. If you go out to the west side, there's the Ko'olina resort and I hear the lagoons there are really nice. They also have this
Paradise Cove Luau there and the Ihilani resort has a spa. Ko'olina golf club also has Roy's restaurant which was pretty good. Lots of great golf courses in Hawaii (though I don't play well enough to go to any of them) if you're into golf.
If you want some upscale dining, John Dominis has some great food, and I recently went to
Nick's Fishmarket that had some great food as well (and as a bonus, I think Nick's is owned by Pat Bowlen, the owner of the Denver Broncos).
Oh, and since this is Memorial Day, it'd be hard not to mention the Arizona Memorial if you've never been there.
Hope you enjoy your vacation.