Gumbo file powder is a necessity for cooking authentic Cajun cuisine. Quite simply, gumbo file powder is the powdered leaves of the sassafras tree. When ground, they smell somewhat like eucalyptus or juicy fruit gum. Long before the use of file powder for Creole and Cajun cooking, American Indians pounded sassafras leaves into a powder and added them to soups and stews. In addition to contributing an unusual flavor, the powder also acts as a thickener when added to liquid.