Another peice of vitally important equipment that's being ignored is your mode of transportation. Nothing protects you better from zombies than being able to stay away from them, and any single location will eventually become more a liability than a defense. When choosing your vehicle, you must weigh many factors-
Speed: Surprising to many first-time survivors is that raw speed is of little use or need, so long as you can reliably maintain a speed greater than that of the zombies. Higher speed is certainly desired for emergency rescue, but is otherwise a low concern.
Torque: Conversely, significant engine power has many uses - freeing stuck materials, towing more supplies, carrying large numbers of people, mounting heavier armor, and plowing through waves of flesh.
Rough Terrain Capability: Useful for immediately obvious reasons, and will become more obvious over time as man's great works crumble and fall. Escaping into open country is also a good strategy, and having a vehicle that can take you there is just sensible.
Size: Obviously, being able to carry more survivors or supplies is desirable, but remember that being able to maneuver through tight spaces, or tight crowds, will be necessary eventually. Even a single person vehicle will need room for your extensive lone-wolf pack of tools and crippling sense of guilt. An ordinary four/five person vehicle is adequate for most survivors. Large groups of survivors will need multiple vehicles for insurance and flexibility. Finally, don't make the mistake of open-topped cargo space - even a dump truck can be climbed into.
Defensibility: This is much more dependent on the nature of the threat, but should always be in the front of your mind. Against "classic" shambling hordes, a modern automobile is quite safe as long as the doors are locked and the vehicle doesn't roll. If the threat possesses any great measure of strength, or god forbid intelligence, your improvement efforts must increase dramatically. Anti-roll outriders, sweeper bars, and a spacing cage will likely be needed. Never forget the utility of some simple angle-iron and chicken wire. Also, it needn't be said, but however stylish and apropo it may feel, a motorcycle is suicide.
Fuel Economy: Almost mutually exclusive with all of the above is long running time. Gasoline will immediately become painfully finite, and stopping your progress is never safe. An alternative fuel vehicle is similarly problematic - lack of infrastructure will render most advanced engines useless very quickly. Being able to carry abundant fuel with you is great in theory, but is heavy, and may wind up being just more bulk you can't eat. One option often overlooked is animal power - a horse needs only grass from the roadside. This still carries it's risks from frequent stops and possible injuries. Of course, heavily urban areas may not have this option, and if the zombies are attracted to animals as well as people this is right out.
Ultimately, the best option would be a light-frame truck with a hybrid gas engine, or better yet diesel, stripped to it's bare essentials then built back up for defense. Reproduce as many as needed and possible for your survivor group.