This should be in your owner's manual but usually most manufacturers give you about 2 gallons in a reserve. My rule of thumb in ANY car is 50 miles after the light goes on MAXIMUM and that's pushing it.
The light really means "find your next gas station, start looking now". Relying on the light is not only not so reliable (what if you don't notice it right away, how far have you driven already, are you going up a hill or down a hill) but also some sediment can collect at the bottom of a gas tank on a 5 year old car and you'd just be sucking that up all the time.
Another way to figure this out is this: As SOON as your light comes on, fill up immediately and see how much gas you take. Your TOTAL capacity is 17 gallons on that car. So if you take 15 gallons as soon as the light comes on, you know you have about 2 gallons reserve. This isn't completely accurate and may be off by one half gallon or so, but it's about as good as you'll get.