Not sure on a "if I were running nothing but the car" senario.
But, I've done it twice in an S10 Blazer.
One time I made it about 100 miles(Tracy, CA to Gilroy, CA) with headlights for about 30 miles of it.
Another time, I made it from Gilroy to San Deigo(approximately 420 miles after the alt blew) using two batteries in the middle of the night <IMG SRC="smilies/eek.gif" border="0"> The first battery made it to the industrial LA(BTW, lovely place to change a battery <IMG SRC="smilies/biggrin.gif" border="0">).... this includes a stop for gas which involved starting the car again. The second battery was a red top Optima and made the other 200 or so miles.