I love that "all" emergency preparedness discussions in the P****** et. al. family return to one subject: guns. It is way more interesting to talk about guns than millett and red winter wheat (or rice and soy flour). So... I figure I'll add my two cents to the discussion.
If you are planning on hoarding tons of food for Armageddon you will definitely need a good gun for fending off the hungry hoards...I recommend a minigun with water/oil cooling. On a cheaper budget I suppose a high powered shotgun would be the second best. The added benefit of the shotgun is that if the zombies are coming, they are good for stopping zombies (whereas the efficacy of a minigun is unknown at best). The transportability of a minigun is a major issue, as well as cost. The best bet is probably to wait until just after Armageddon and then steal one from a military installation. Another alternative is to buy an assortment of high caliber rifles and shotguns, which are cheaper and have the same efficacy as the minigun, but then again you'll have to have a number of different triggermen, which means sharing the hoarded food. Also, prior to Armageddon you'll have to avoid those pesky ATF guys (think Ruby Ridge and Waco). Also, you'll want to get a gun with a very common round size because you're likely to need ammo at some point and nobody will be making it any more so you'll have to scrounge what you can. If you have to make your own ammo, I know a guy who developed a great (gluten free) gunpowder recipe just before blowing himself up. If I can find it I'll add it to the discussion.
Hope that helps,