My daughters and I were just in Flagstaff last month which is about a 2-1/2 hr drive for us.

Longest car ride was probably from Maryland to Idaho and back again when I was a young teen. Instead of a direct route, we went a more southern way there and on the way back we headed north through Canada, went across and then down through New York.

I've also done the Maryland to Texas trip straight through (no overnight stays) -- took us about 24 hours.