My very favorite purchases at Costco (because I think they save me the most money) are:
- the big bag of chicken jerky for my dog (it's $9.99 at Costco and easily the size of 4 of the bags they sell at my local pet store for the same price)
- Odwalla fresh juices (either about $4.75 for a half-gallon or about $9 for a flat of 12 individual-size bottles that I love to grab for breakfast)
- bananas -- $1.29 for a whole bunch (about 10)
- organic, free-range eggs (about $3 for 18 eggs)
- and, hot house tomatoes (a plastic box with about 18 small tomatoes for about $5).
Non-food things that I often buy are magazines (30% off cover price), movie tickets, iTunes gift cards, boxes of greeting cards, flourescent light bulbs (you have to buy 8-10 at a time, but they are significantly cheaper than the hardware store), and nice cushy socks.
Have fun shopping! A good way to start or end your trip is to get a frozen latte (like a Frappucino) at the food court for $1.25. Yum!
p.s. These are California prices.