The low fuel light is set to come on when there is approximately 3.3 US gallons left until the needle reaches the E... at which point a small (undefined) reserve remains. I guesstimate that when the light comes on I have about 4 gallons of fuel remaining.
So that is really your key to not running out of gas... not how much you pack in the tank!
One of the things I like to do is know how far I can reliably go after getting the LF light. There are simply times in life when a fuel stop is not in the cards right when the light comes on. I will go 40 to 50 miles on the LF light before getting antsy.
How far did you drive into the LF light on this occasion?
Edit: one caveat: some believe the fuel pump is cooled by immersion and can be damaged by running with low fuel. Personally, I think the fuel pump is cooled by the fuel flow, so I don't worry about the fuel pump and running the tank low. As usual, YMMV.
