Once the Zombie out break occurs, you are going to have to be ready. You have to be ready to run, you have to be ready to fight, and you have to be ready to take care of yourself for the duration of the crisis. When the shit hits the fan (SHTF), you don't have time to run around gathering everything you need. The zombies are coming and you need to have everything available at your fingertips. That's why you need to get a kit!
|A Japanese Earthquake Survival Kit - Photo By David Pursehouse (Flickr: Earthquake Survival Kit) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
What should be in your kit? You'll need supplies for food, water, shelter, medical needs, self defense, communications, and gear maintenance.
You should even consider having multiple kits. One for your person, one for your vehicle, and one for your home. The personal kit should be enough to sustain you for a limited time away from your group. The vehicle kit should sustain the vehicle and passengers for an evacuation. Since the vehicle is doing the lifting, it can carry more gear. The home kit is for sheltering in your home for a long period of time.