Groceries are expensive on Maui. You can easily pay twice of what you pay at home for your food, if you shop at major grocery stores – Safeway, Foodland or Star Market. When we prepare for our Maui trip, I always write a list of products to buy. My first stop on the way home from the airport is Costco. And you’ll need some space in your car for that!
Maui Costco is located on Dairy Road, near the Kahului airport:
http://www.costco.com/Warehouse/LocationTemplate.aspx?Warehouse=119
I don’t know how they achieve it, but prices in Maui Costco are the same as in Mainland ones. Don’t forget to buy your sunscreen here – you’ll pay 2-3 times more at other stores. If you plan to snorkel, and would rather buy than rent, Costco has excellent snorkel sets for adults and kids.
I always buy two salad kits and a rotisserie chicken for the first night plus a bottle of wine or beer, and we have a very relaxing sunset after the trip. When you buy vegetables at Costco, always note the expiration date, and buy the freshest. Veggies spoil easily in the hot and humid climate, and they may already come a bit wilted before being placed in the refrigerators.
There also is a Kmart near Costco and Wal-Mart further south on Dairy Road. In case you forgot that special pillowcase or a pair of reading glasses, it’s best to visit one of those instead of the local stores, where it’s more expensive.

