The regional sandwich tradition in France maps onto the regional cheese, sausage, and bread traditions, and reading through the list is a tour of how the country eats outside of Paris. The Sandwich Alsacien runs to dark seigle, choucroute, and a slice of saucisse. The Sandwich Breton uses galette buckwheat batter as the wrap, fills it with ham and gruyère, and folds it shut on a hot plate. The Sandwich Niçois borrows from the Pan Bagnat but doesn't soak. The Sandwich Lyonnais is a baguette with rosette and a Saint-Marcellin smeared underneath.
Further afield the regional inflections get stronger. The Sandwich Ch'ti is a working-class invention from the Nord — a baguette with maroilles (the famously pungent washed-rind cheese), thin-sliced ham, and a pickled cornichon to cut the salt. The Sandwich Auvergnat layers blue and brebis cheeses with thin slices of mountain ham. The Sandwich Berrichon adds rillons and a leaf of frisée. The Sandwich Périgourdin lands a slice of magret over a smear of foie gras for those who treat regional cuisine as a contest.
Each of these is a small argument about what a sandwich should taste like in a particular corner of France. None of them travel especially well — the maroilles in the Ch'ti is funkier than most cheese-shop fridges allow for, the brebis in the Auvergnat needs to be cut on the day it's eaten — and so the regional sandwich tradition stays mostly regional. Which is, on the evidence, exactly how the regions like it.