Mickey Mouse mugs, political buttons, first edition comic books, bottle caps, and trading cards--the New Antiques are often yesterday's smock. Gilbert appraises the collector's scene, separating the more speculative items from blue chip investments. She's seen a marble go for $200, a set of Miss Rheingold beer cans bring in four figures. She offers these words of caution: be wary of restorations and newfangled ""limited editions,"" and don't expect to triple your investment by buying just anything old. Attention: willing to trade first edition Kirkus bulletin, hand-cranked on genuine old mimeograph machine, for 900 bottle caps or one sheet-tin weathervane.