What ingredient appears in all sandwiches listed except for the J.J.B.L.T.?

The correct answer is mayo, as it is not included in the J.J.B.L.T., which is specifically a sandwich consisting of bacon, lettuce, and tomato. Unlike other sandwiches that typically have mayo as a common condiment, the J.J.B.L.T. focuses on highlighting the bacon and fresh vegetables without the addition of mayonnaise. Recognizing this detail shows an understanding of how specific ingredients are chosen for certain sandwiches to establish their unique flavor profiles.

In contrast, sauce, tomato, and cheese are ingredients commonly found in many other sandwiches. For example, many sandwiches at Jimmy John's might feature a sauce or cheese alongside tomato, making these ingredients less distinctive in terms of absence in the J.J.B.L.T. It's important to consider not just what ingredients a sandwich can contain, but also what might be intentionally left out to create a specific taste experience.