The Sandwich Thon-Crudités is the full deli combination: tinned tuna and a whole counter's worth of raw vegetables in one baguette. The tuna is flaked and lightly bound, usually with mayonnaise, and then layered with sliced tomato, cucumber, shredded carrot, lettuce, sometimes ribbons of raw onion or a few rounds of hard-boiled egg. Where the plain tuna-mayonnaise sandwich is a single dressed filling and not much else, this one is a built sandwich with structure to it, a base of bound fish under a salad's worth of fresh produce. The crudités are not garnish here. They are half the sandwich, and the name puts them on equal footing with the fish.
The logic is the contrast between the soft and the crisp. Tuna out of a tin is mild, dense, and uniform in texture, and on its own it goes monotonous fast. The raw vegetables answer that directly: the cucumber and carrot bring crunch and cold water, the tomato brings acid and sweetness, the lettuce brings volume and a clean snap. The mayonnaise binds the tuna and bridges it to the produce so the layers read as one sandwich rather than two foods sharing a baguette. The risk is the same one every vegetable-heavy sandwich runs: a cut tomato weeps, shredded carrot holds water, and a wet base ruins the bread from the inside. The successful version manages this by salting and draining the tomato a moment before it goes in, keeping the wettest elements off the crust, and mounding the filling loose rather than packing it dense.
The bread does the structural work the soft, wet filling cannot. A baguette with a firm crust and an open crumb holds the dressed tuna and the produce without going slack, and there is no warm component and no reason to wait. A tuna-and-crudités sandwich sitting in its wrapper soaks through within the hour, and the lettuce is the first thing to wilt.
Variations move along the vegetables and the bind. A version with more egg and olive leans toward a salad-on-bread; one bound with a lighter vinaigrette instead of mayonnaise reads fresher and sharper; one with the tomato left out keeps better and travels further. Each holds the tuna-plus-raw-vegetable structure fixed and changes only the produce or the dressing. It belongs with the fish sandwiches the catalog groups under Baguette Poisson, and its specific contribution is the full combination: not tuna alone but tuna carrying a salad, where managing the water decides whether it holds together.