I have a 1995 tr4...I called toyota and they told me when the fuel light comes on { flat ground } you have about 15 miles of drive time left...this seems right , because the other day, my light came on...and I watched the trip odometer...I got about 14 miles and my engine stopped running...luckily I had just pulled into the gas station and was able to drift up to the gas pump..
Now..keep in mind...when the fuel light comes on...you may have close to 2 gallons left in the tank...but about 1 gallon of that is unuseable because it sits below the gas tank inside fuel tube....this is done to make sure any contaminants , debris sits at the bottom of the tank in that unused gas and doesnt get into the fuel lines.
so this basically means you would have about 1 gallon of fuel left in the gas tank , even if you run the engine until it stops running from lack of USEABLE fuel in the gas line.