Honda And Acura
With all the Honda and Acura cars I've driven the light goes on when there's two gallons left. Press the tripometer when the light comes on and you can track how far you've gone. The modern cars even calculate your mileage for you, so you have a good idea how far you can get. Note that the gas pump is cooled by the gas remaining in the tank, so doing this too often can be expensive entertainment.