The milage after "empty" differs a great deal between Diesel and Gas Golfs.
I routinely get 90 highway miles in my TDI(diesel) Golf after the light goes on...but then...the thing gets 47mpg on the highway! (My gas-Rabbit gets 32mpg highway) Bonus on TDI's: there is a small pressure-release valve just inside the fuel intake. Fill the tank, then depress that little valve. Listen closely, you can hear a little "whoosh". You can now squeeze another liter of diesel in! Enjoy!
squeeze a litre in? try squeeze 10 litres in! i got over 100km more to the tank when i discovere that little wonder