If you have a map of Oahu that'll help. You can get one on Yahoo Maps.
Sam's in in Aiea or Pearl City, I'm not sure which. It is basically at the intersection of H1 and H2. It takes just under an hour to get there. It is open 9am to 9pm, I think. It is a good size store, but then I don't know the choices of sizes in Sam's Clubs stores. It has three big banks of
freezers/coolers. They have a fish/sushi department, and the normal other stuff. Sam's tends to be slightly cheaper than Costco. Sam's is below a shopping area that has:
a craft store, Old Navy, theaters, party store, and other shops. There is a Home Depot across the street.

Costco has several stores on the island. (3 I think) The closest one is off exit 2 on H2, so it's about 2 miles from Sam's club. There's also one by the airport, and one in Wailua? South of Kaneohe. The one off exit 2 was built during the past three years. It's an okay size Costco. I can't remember if they have the 1-hour photo or not. I know that Sam's and the airport
Costco do. We have memberships to both since there are things that you can't get at the other one. I can't say that, that's an effective way to spend the membership money, but we still have both. :-) It is open at 11am for regular customers, and 10 or something for business customers. Costco is by itself, but the Waikele Shopping area is nearby with clothing outlets (Carters is really fun), and a hardware store (used to be Eagle), COMP USA, a pet store, Walden Books, a party store, a McDonald's, Chili's, K-Mart, and other stores.

Walmart is the biggest NON-GROCERY Walmart that I have seen. It is open 24 HOURS a DAY, which makes Christmas shopping a pleasure. :-) It's where most people go to get all their non-food items. You can get some little bits of food there, and sometimes the prices on them are super compared to the grocery stores. It has the usual selection of holiday items to purchase which makes shopping really fun. :-) It is 45 minutes away in Mililani, exit 5B off of H2. It has a McDonald's inside the store. It is part of a shopping mini-mall area that has Burger King, Kentucky Fried, Chili's, Walden Books, a drug store, a grocery store, lots of specialty shops, a gas station, a hardware store, a restaurant, and other eating spots, and a nice new Theater with 8-12 movies. Don't know how many.

Produce is high at Foodland. Costco and Sam's seem to be closer to mainland prices, so we stock up when we go. I usually spend $200 to $300 a trip. I also take coolers in the van. That's a different way to shop than my mainland shopping was. We usually hit Sam's or Costco and Walmart on one trip. The minivan is crammed full with stuff. You usually plan an hour each way to drive and an hour or two at each store depending on shopping style. Thus the whole thing makes an all-day adventure. You can do it while the kids are in school and be home in time to greet them or have them unload the groceries. :-) They are usually willing to help do this since there's food involved. :-)

I think the big stores are resonably priced, but expect that costs will be higher than the mainland. The Flea Market (around the Aloha Stadium) is an excellant place to get clothes. I can buy Aloha shirts for $10.00 each. I can get T-shirts from 5 for $20.00 to 10 for $20.00 depending on the size and if it's embroidered or silk screened. Most people just wear T-shirts year round and shorts, capris, casual stuff. The guys wear slacks on campus, and Aloha or casual business shirts. You can also buy ladies dresses at the flea market, backpacks, hawaiian type food (macadamia nuts) and leis. It's really fun to shop there. :-)

For those into cake decorating or crafts: They have some Wilton at Wal-Mart, and at Ben Franklin Craft store. There's also a Wedding type store down in Honolulu that has TONS of stuff. I've seen a good selection of cake stuff there. It seems that none of the stores stock all the stuff you want so you buy something here and something there. It's probably one area that you'll want to keep a list of for visitors to bring from the mainland. I know that spool o ribbon was cheaper at craft stores on the mainland. They don't have Jo Ann Fabrics and crafts here and I really miss them. They were reasonable and had a good selection. I usually look up what sewing patterns I want and have my daughter ship them to me. Here the cheapest pattern is half-price. I can get the 99 cent or 1.29 or 1.99 at the worst at my daugher's, and shipping is pretty cheap on patterns. Friends usually ask if they can bring anything, and I've taken them up on lots of stuff. :-)