One of Walter Cavanagh's credit cards—the sterling silver one issued by a casino in Reno—once set off a metal detector at a Houston airport. When security guards took a precautionary look in his briefcase, they found more than 900 other charge cards. Once again, Cavanagh, whose passion is plastic, had not left home without it.

Cavanagh, a Santa Clara, Calif., financial planner who gives advice on real estate investments, has the world's largest credit card collection. He has green cards, gold cards and platinum cards; he has cards from every state in the Union as well as from Britain, Canada, Norway, West Germany and Mexico. "I can charge ice cream in Texas or a house on the East Coast," says the 45-year-old bachelor. Not to mention cookware in South Carolina, tall-girl dresses at a shop in San Francisco or anything he wants at Sweezy's Department Store, "wherever that is," says Cavanagh.

Cavanagh's pursuit of plastic began 16 years ago when he bet a friend that he could collect the most cards within a year's time. "I thought maybe it would take 10 to 12 cards to win," he says. Instead, he won the bet—dinner at a fancy restaurant—after accumulating 143 cards. That also won him his first entry in the Guinness Book of World Records and set him on his way to becoming the Imelda Marcos of credit cards. "Some people read; I fill out credit applications," he says. "A lot of times I'll receive a letter back saying I already have that card."

Usually he applies for one or two cards a week, but one winter when he was bored he applied for 300 in a month. Most are strictly collector's items that never see a countertop. "Ninety-five percent of these cards have never been used," Cavanagh says. "I never sign them. They're virgin cards."

Nor is he prodigal with the plastic he does carry. Cavanagh usually packs only two or three cards with him at a time and settles up promptly every month. "I'm conservative. As soon as I get the bill, I pay it," he says. "Even my car is paid for."

The 1,205 cards in his collection are worth about $1.5 million in buying power, Cavanagh estimates, but he's not satisfied. "There are over 10,000 credit cards in the world," he says. "My goal is to get them all."