Long ago when I arrived in France I met Polly Platt, author of the wonderful French or Foe?, a book I recommend to all expats in France. Polly died a few years ago, but her book lives on. As it is more about the French character than about ephemeral things, French or Foe? is still extremely useful to people coming from a very different mindset (Americans, Brits, northern Europeans, Japanese...).
One of the surprising things Polly explained was the importance of champagne. Even students or the unemployed will produce champagne for important occasions. In much of Paris, and certainly in my neighborhood, champagne is still de rigueur if you entertain. It is usually served as you arrive at a dinner party or cocktail. The party we went to last Saturday night, for example, was in a top floor walkup not far from Saint-Germain. The host and hostess are in their twenties. Here's their back hall, an hour into the party.
Polly told me that an anxious young American once asked a French friend of hers, "What do you do if you can't, like, afford champagne?"
"You don't invite people over," was the implacable response.