A tomato sandwich might be a curiosity to some people, but to those who grew up in the Southern United States with a taste for tomatoes, it is one of the best dishes on the planet. Tomato sandwiches are exactly what they sound like: tomato slices sandwiched between two slices of bread, plus some mayonnaise. Of course, such simplicity warrants excellent ingredients, and although the tomato is the star of the show here, even the type of bread you use matters.
Before you reach for a $10 loaf of sourdough (America's choice during tough times) or an artisan brioche, know that the majority of Southerners will agree that the absolute best bread for a tomato sandwich is soft white sandwich bread, the kind you can pick up in any grocery store, not a fancy French bakery. You don't want anything to take away from the flavor of your tomato, like a nutty or flavored bread, and your teeth should sink right into the sandwich, so it's not the time for a chewy crumb. In addition, white sandwich bread works like a sponge to absorb some of that glorious tomato juice that will undoubtedly ooze out of the fruit as you bite into it.
In addition to the bread, you should aim to use the biggest and best tomatoes you can find, preferably homegrown or heirloom varieties from a local farmer's market. These also happen to be the best types for BLT sandwiches. As far as the mayonnaise goes, Duke's brand is king in the South, but any good mayo will do.