Comment by CalChris

In the scene which sets up the Marseillaise scene, Yvonne comes into the bar with the German officer and he orders the only drink mentioned by name in a movie with a whole lot of drinking, the French 75, named after the French WWI 75mm field gun.

   gin, Champagne, lemon juice and sugar

https://en.wikipedia.org/wiki/French_75_(cocktail)

Yvonne finds her moral core when they play the Marseillaise just as Rick later finds his when he has to make a choice.