Definition & Meaning of "pub sub"in English

What does "pub sub" mean in Southeastern US slang?

The structure is a clipped shortening of "Publix Submarine," where "Publix" is a supermarket chain and "sub" is short for submarine sandwich, combined into a catchy abbreviation. It is used in the Southeastern United States, especially Florida, to describe a sandwich purchased from the Publix supermarket chain, often made to order with a variety of meats, cheeses, vegetables, and sauces, widely considered a regional staple. People typically say "I'm grabbing a pub sub for lunch" or "Pub subs are the best thing about Florida."