courtesy gallon

That extra ~1 gallon a car really has when the low-fuel light shows up on a car's dash. You think you're totally out of fuel but you actually have another gallon to go....it's a courtesy gallon!

I have been driving on this courtesy gallon for a little too long; I should probably go to the gas station.

I was afraid about breaking down on the road but remembered I still had my courtesy gallon!