Accordion I can answer. Italian migrant workers brought accordion into the country in the very early years of the 20th century. There had been an earlier influx of Auvergnat workers, and they liked to dance to bagpipes, so there was a lower-class kind of dance in cafes called Bal Musette. For a while the bagpipes ( cabrette) played alone, then with accordion, and then the accordion took over, one kind was developed to become more chromatic, and by the 1920's the accordion had become the predominant popular instrument , especially the chromatic kind for playing Bal Musette. The music is still around, still called Bal Musette. Characterized by lots of fast waltzes, and kind of staccato mazurka called a Java, the latter particularly once associated with Parisian gangsters.

The beret and a bicycle full of onions (another French stereotype in the UK) derive in part from Onion Jonnies, Breton onion farmers who cross the Channel to sell onions in the UK. The practice is apparently still alive (just) albeit far reduced compared to the heyday of the early to mid-20th century.

I'll answer the striped shirt one. The marinière is typical of quartermasters in the French navy, but it's also just constantly in style. Here's an article You see them everywhere, and it's totally both sexes--there might be slightly different styles for dudes and dames, but everyone wears it.