For your theme-based hot dog/shaved ice stand it seems that Tiki is real big now. Big Lots and places like Old Time Pottery and Hobby Lobby sell the tiki-like umbrellas and assorted tiki items (lights, etc.).
I would love to have a hot dog stand and shaved ice stand here. The problem is that most of the ball fields here have their own concessions stands (this includes high schools, Little League, etc.).