Here's my Costco shopping list, keeping in mind that I'm married with 3 kids, 2 dogs, and a cat. I have a price book, so if it's on this list, I couldn't find it cheaper anywhere else and, if it's perishable, we use enough of it that it won't go bad.
* Pencils and pens
* Flour tortillas
* Whole-wheat sandwich bread
* Beer and wine
* Organic hamburger and various other meats, frozen and not
* Cantaloupes
* Mandarin/cuties oranges
* 2L soda (unless its on sale somewhere else, because the price isn't that great)
* Frozen organic strawberries, broccoli, and mixed veg with soybeans
* Colby-Jack cheese blocks
* Shredded mozzarella
* Organic milk
* Organic eggs
* Butter
* Kirkland "House Blend" coffee - packaged by Starbucks
* Canned diced, crushed, and paste tomatoes
* Dried apricots or dates
* Tuna
* Olive oil and vinegar
* Lemon juice
* Spices
* Agave nectar, honey, maple syrup
* Ketchup and mustard
* Rolled Oats
* Pedigree dog food
* Ziploc freezer bags
* Giant rolls of plastic wrap
* Laundry detergent, powdered
* Dishwasher detergent, gel
* Granola bars, other packaged snacks, and candy, when I buy them, which is very rare
* Sometimes they have good deals on things that would make good gifts (toys, books, clothes, etc.)