Hardly the perfect shopper's companion, however helpful some of the tips might be--how to calculate BTUs when buying an air conditioner, say, or how to convert porterhouse into both filet and shell steak at one-third the cost. Stossel is Consumer Editor of CBS-TV's New York station, and he has instructive things to say about each of the areas he's looked into: new and used cars, house buying and furnishing, drugstore and supermarket products and prices, travel, financial planning, and, for a coda, ""How to Complain."" But his information is anything but complete: how to shop for heating oil is omitted; except for a brief note on carpets, there's nothing on floor coverings; and to learn anything about such major appliances as washing machines, dryers, and dishwashers, you'll still need Consumer Affairs' Consumers Guide. Even more surprising, given Stossel's 19 pages on the supermarket, is the neglect of unit pricing. Sometimes Stossel scores because he gets down to basics (a warranty is a guarantee by a fancier name), sometimes he's so basic (in Small Claims Court, ""All you have to do is answer questions and tell your side of the story"") that he may deter consumers from learning what they need to know. Adequate only for an overview and some random pointers.