Massive head trauma or severing the top of the spinal cord.

And a real zombie outbreak would fucking suck. Your plans would go to shit, putting you in sudden desperation when you should've been looking for explosives instead of guns.

And in addition, if you think you and your friends would make the best survival squad ever (every group of friends does), keep in mind that you'll probably end up killing quite a few of them just for slowing your group down.

__________________