The term 'Sandwich Staple' refers to four common ingredients used in sandwiches: RYE (3 letters), SWISS (5 letters), TUNA (4 letters), and HAM (3 letters). RYE is a type of grain used to make bread, and is often used as the base for sandwiches. SWISS cheese is a type of cheese with a mild flavor and a creamy texture. TUNA is a type of fish that is often canned and used in sandwiches. Finally, HAM is a type of cured pork that is often used in sandwiches. All four of these ingredients are commonly used in sandwiches, making them staples in the sandwich-making world.