Most Costco members have received the monthly coupon book in their mailbox. Most have glanced at it, found a few things interesting, and then gone to the warehouse without it. A smaller, more commercially savvy group of members treats it as the planning document it was designed to be — and the financial difference between those two approaches compounds into hundreds of dollars per year. Costco officially calls it the Member-Only Savings booklet. Most members call it the coupo