What it means. If upon leaving a BJ's Wholesale Club, Costco, or Sam's Club your shopping cart overflows with way more items than you ever intended to pick up and you're left wondering how you ended up with enough cheese sticks to feed every elementary-school kid in town and so many Post-its you could paper Hoover Dam, you're experiencing a big-box binge.

While the New England Journal of Medicine has not yet documented this condition—in which a shopping-induced euphoria is wiped away by the reality of yard-long receipt handed over at checkout and a hefty addition to the credit-card balance—anecdotal evidence suggests it is widespread. A colleague of mine recently went to Costco needing to stock up on paper goods and headed home with those items plus a 10-pound bag of organic carrots, a two-pound block of Vermont cheddar, a case of organic chocolate milk, and a tons of other stuff that somehow ended up in the back of his minivan.

Why the buzz? Much of the U.S. economy has slowed to a crawl during the recession. But, like repo men and foreclosure auctioneers, big-box stores are busy. For February, Walmart recently reported a 5.1 percent year-over-year increase in same-store sales, exceeding Wall Street's expectations. BJ's same-store sales were up 8.2 percent, and Costco posted a 5 percent gain (not including fuel). American consumers have cut back on discretionary spending but are still streaming into wholesale clubs and often walk out with more than they planned to buy. (Big-box bingeing knows no borders. The image shows the opening of a Costco in Japan.)

"Club stores are doing pretty well in this down economy because they focus on value," says Consumer Reports' shopping guru Tod Marks, whom you might know as Tightwad Tod. Big-box bingeing occurs because, says Marks, these retailers "make it too easy to run up your bill with deep discounts on everything—books, video games, garden supplies, gourmet coffee, small appliances . . . you name it." Indeed, an informal poll of club shoppers who visited ConsumerReports.org suggests that as many as half spent more than they intended on their last trip.

To avoid big-box binges, keep this "CHECK" list in mind:
Carry cash. It's easy to overspend when you pay with a credit card. But using cash can help you avoid needless purchases.

Have a list. We're now in the era of spartaneity, not spontaneity. A shopping list might keep random items from fattening your bill. Consider adding prescription meds to your list. "We've done numerous price studies that show warehouse clubs, in particular Costco, to be one of the cheapest sources of medicine," says Marks.

Enlist friends and family. Splitting large purchases with others lets you take advantage of bargains without overloading on bulk buys. This is especially true for perishable items. "No matter how low the price is on that monster box of fresh apples or peaches, it's not a good deal if you can't use them up before they spoil," says Marks.

Comparison-shop. Warehouse clubs don't always have the lowest prices on food. That's because supermarkets sell some items at or below cost to lure you into the store, hoping you'll purchase other marked-up items once you're inside. Clubs don't play that game, so their everyday low prices can't always compete with the prices on loss leaders in supermarket promos.

Know how to spot a true bargain. At Costo, a .97 at the end of a price generally indicates discontinued or slow-moving products. At Sam's, a C at the end of a price number denotes canceled, heavily reduced items.—Daniel DiClerico