To expand on the above comments, the reason one gallon of fuel is not enough to get the car restarted is because you are now sitting still. While the car was running the movement was able to slosh fuel around so it could be pulled into the fuel system intermittantly. Sure, there would be periods of time when only air could be pulled, but for some period of time you'd get enough fuel to run the car.
Now that you are sitting still there is no sloshing action, and without that sloshing the fuel can't reach the tank strainer. You have to overcome that with several gallons of fuel, not just one gallon.
Does the fuel level gauge show up down at the "R" or lower? I learned the hard way not to put too much trust in the "low fuel" light coming on. One time it didn't.
Ken300D