This is a vintage "Souvenir of your flight with Lambert Field's Oldest Operator."  The oldest operator was presumable William B. Robertson of Robertson Aircraft Corporation.  The ticket is likely from the early 1940s.  It measures approximately 3.25 by 2.5 inches.  It is protected in a clear plastic frame that opens with screws at the sides.  The ticket can be removed from the case.  Good vintage condition.