A bicycle.
Why? Because most of this stuff runs of gas or some sort of other fuel source that will eventually run out. If a zombie apocalypse was to happen, I'd probably be one of the only ones left, save for maybe my boyfriend, but he'd be riding on a bike right beside me. I wouldn't need to have a vehicle that carried multiple people.
It's lightweight and doesn't run on anything. Hopefully by then I'll be in shape so that I can ride one. Then again, it would depend on what kind of zombies you're talking about (quick ones, normal very slow ones, special zombies, etcetera.) which would probably elicit another choice in a vehicle.
Besides, you're supposed to pack light in an apocalypse, not have bulky weapons that weigh so much that you waste more energy shooting the darn thing than running from the zombies themselves.
/has read the Zombie Survival Guide
Yeah.