By Jane Bennett Clark
Kiplinger's Personal Finance
Sunday, August 3, 2008

For a reliable bargain on dog food or diamonds, head to a warehouse club, such as Costco or Sam's Club. These clubs limit their margins to 11 to 14 percent, compared with 25 to 30 percent at supermarkets and mass merchants, according to Michael Clayman, editor of the trade publication Warehouse Club Focus. Annual membership starts at $40 at Sam's Club and $50 at Costco. Both clubs offer upgraded memberships, starting at $100 a year, that give you a 2 percent rebate on the year's purchases.

But you won't save much money if you get sidetracked by the bling and the flat-panel TVs. Here's how to make the most of a trip to the warehouse (and spend the least).

· Do your homework. Don't try to bone up on brands and prices amid the kids, carts and chaos. Comparison-shop online before you leave home so you know which products and features you can't live without before you arrive.

· Grab the deals. You can always count on finding a small but decent selection of electronics, fancy food, jewelry and brand-name clothing. But the treasures -- say, a Kate Spade bag or Ralph Lauren coat -- are here today and gone tomorrow. Snap them up right away or regret it later.

· Be prepared to do it yourself. You're on your own when it comes to getting that hot tub off the warehouse floor and into your car. (Order online, and the clubs will deliver). You'll do the installation, too.

· Watch those portions. Warehouse clubs offer better prices because they sell in bulk. But it's no bargain if the food goes bad -- or if you bulk up by eating it. Save money and your waistline by resisting the temptation to race through an entire tub of rocky road ice cream.

· Gauge gas prices online. Warehouse-club deals on gasoline are good but not always the best. Before you drive 10 miles to Costco, check local prices at GasBuddy.com.