A guy opens the front door of the car for a girl to ride shotgun and she says " I've never sat up here before" What is the purpose of the "up"?
"Up" here reinforces that it means the front seat.
We often say "sit up front." (We don't, however say "sit down back.")
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
thank you!