Check out this 1957 ad for Avis' Fly & Drive Ticket which gave you a 24-hour rental including gas for $10. That's a pretty sweet deal. You could purchase the ticket right from the airline and have an Avis car waiting for you at the airport when you arrive. Seems pretty convenient if you ask us.
It's also interesting to note the airlines that offered this deal. Out of the 22 airlines listed in the ad, only 8 (American, Continental, Delta, Frontier, Northwest, Piedmont [a.k.a. US Air Express], Southwest, and United) still exist today--7 if you take into account the merger of Delta and Northwest.
Oldies but goodies like TWA (once one of the world's largest airlines), Braniff, Ozark and Western are no longer with us. RIP.