I think the largest cultural difference is just the openness of Americans versus the closed-off nature of the French. I feel that the French are very introspective and less willing to strike up conversations with strangers. Along these lines, the French also smile much less than Americans, and a smile is seen as an invitation to talk. For example, if you smile at a stranger on the street or metro, do not be surprised if they immediately run up to you and ask what you want.
In terms of time management, the French seem to be much less pressed than Americans. They stop and frequently take pauses throughout the day to reflect, or share a meal with a friend. For example we are supposed to start work at 10, but most people stroll in between 10:05-10:45 without explanation. Along these lines, the French place a lot of value on separating the different aspects of their life. In America we often will eat on the go or at our desks, but the French really make an effort to separate work and personal life.
For the average citizen, the French live in much smaller quarters and have much less material items. As cliché as it sounds, they really prioritize quality over quantity. I think that random people on the street would express the notion that American’s love excess–food, clothes, objects. They also tend to generalize the United States as being a compilation of “New York, Miami, and California,” which I find extremely funny because they are such small parts and cultures and do not accurately represent the American demographic.