They could have made a torch. *spoilers*

Take the baseball bat, wrap one of the blankets they had hanging over the windows around it, cover it with the liquor they were downing and then use the lighter they were lighting their cigarettes with and, wholla, there's a torch. Mickey could have set a bunch of the zombies ablaze from the sunroof before attempting to find the keys and then used it to fend off the zombies on his way there, which also could have prevented him from being bitten.

My horror movie blog:
http://thebloodypitofhorror.blogspot.com/