While I wholeheartedly support the notion of emergency preparedness, and having a stash of food, water, and yes, ammo stores for either a bug out or defense scenario, but there's a degree of sensationalism that surrounds the whole "zombie apocalypse" scenario that just is a bit hard to buy into.
Scare tactics and fear mongering aside, I would suggest considering possible versus probable scenarios and plan/budget accordingly. Here's how I rank things in order of importance:
1. Ammunition for self/home defense
2. First aid/emergency kit (aspirin, antibiotics, compression bandages, antiseptic, etc)
3. Three day supply food/water packed for mobility (BOB)
4. Three day supply of food/water (homesteading)
5. Seven day supply of food/water (homesteading)
6. Ninety day supply food/water
7. Six month supply food/water
Depending on how paranoid you are, it may also make sense to do a little reconnaissance in your area and planning with family and loved ones. Even if others don't do your level of preparedness, if they know where to go to connect with you, that is a step in the right direction.
The whole concept of bugging out is one that is so overblown it's sad. Great, you've got a BOB, but where the hell are you going to go? No one really talks about alternate locations, preparing them for your arrival, and planning routes and means of getting there in multiple scenarios (consider flooding, snow storms, extreme heat, traveling by vehicle, on foot, etc.). Who else is going to know about this alternate location? Under what circumstances is the alt location better than your primary?
It also bears mentioning that even the above list is assuming several other criteria are in place such as heat, power, your own personal health (could you handle the rigors of hiking, trekking with a 75lb ruck sack?), the health of loved ones, clothing, etc.
I know some folks that have taken it to the Nth degree where they train n defense scenarios with their pack on, have food stores shrink wrapped and buried in PVC tubes and various geocached points between various places that have been identified as bug out locations, and have literally ammo stores coming out the }%#! in each location, as well as the materials needed for reloading at each location. (Wish I had that kinda money...)