Wow. Bike Snob really does know it all:

"But let's be honest--part of the bicycle's appeal is its swift mobility. What cyclist hasn't fantasized about living in some kind of Apocalyptic wasteland with only his bicycle and his wits to keep him alive?"

http://bikesnobnyc.blogspot.com/2008/10/anywhere-anytime-cycling-and-mobility.html

Seriously, the bike would totally be the way to go -- all those empty cars jamming the roads and you and your trusty cross bike ready for anything. You can go fast enough on the knobbies to outrun the mutant zombies, right? Think how much MORE awesome '28 Days Later' would be with bikes. You could do a whole chase scene thing with Cillian Murphy et al doing freestyle BMX through London, jumping staircases, revolving in mid-air FOR THEIR LIVES.