If you go to the Bargain Bank desperately needing a jar of peanut butter pre-mixed with swirls of jelly, of a type discontinued several years ago, you're probably going to be disappointed. The store's stock turns over so fast, and is so varied, eclectic, and random, that the most successful shoppers enter with a Zen cast of mind utterly uncontaminated by preconceived notions of what they'll find. But with the proper attitude, treasures can be found. The Bargain Bank -- which really does occupy an old bank building -- buys overstocked, discontinued, outdated, or for some other reason discarded merchandise, then passes it along to you, the consumer. One shopping trip not long ago produced a bale of diapers with unobtrusive rat nibblings at the bag's edge; the rat didn't harm the diapers and brought the price down by half. Yesterday's expensive perfume is a steal here, as is the occasional jar of pre-mixed peanut butter and jelly. But you can't count on either; instead, enter with an open mind, leave with a surprising bargain.