As a fellow Jeep owner (2004 TJ, {waves - lol}), I was sitting here wondering how you "fill up" a Jeep with only $25.00 (@ approx $2.00 per gallon - that'd be 12.5 gallons of gas per fill up). So I googled things - found this:

http://www.jeepforum.com/forum/f9/gas-tank-size-249444/

Of course, that whole discussion just throws a bunch of wrenches into the works; maybe you do have the 15 gallon tank on a older model (newer JKs have much larger tanks supposedly)? And apparently there's still more in the tank even once the light comes on (a few gallons reserve)?

I've never "buried the needle" on my Jeep yet, so I have no idea what size tank I have.