Like in many countries, the French have succumbed to having cereals and milk for breakfast.
But in my view nothing beats butter tartines or croissants dunked in coffee.
It has also become uncommon to drink wine at every meal, and people also drink less when they do have wine. It used to be that the consumption was close to one bottle per day...
But it should also be noted that the amount of alcohol in wine has increased during the period. It's 12+% now while it was about 10% in 1950 (not sure how much difference that makes, but still).