Not a bad niche topic you've picked. Lots of interest in that sort of thing these days. Are the domain names you listed all dot com TLD? Or different extensions? That would make some difference in how they rank.
For strategy, there are at least three options you could try:
1 - Set up a blog on one domain name and 301 redirect the other names to that one name (simple, might be a good way to start); if you go that route for now, which name to use would depend on the TLD's
2 - Set up two different blogs on two different names and you can do a lot of A/B testing, compare results, experiment on the B site, then promote things that seem to work to the A site, etc. (a bit more work, you really want to make the blogs look different from each other and have pretty unique content between the two)
3 - Set up a small group of sites that feed each other, kind of expanding on option 2, but as an example you could set up a blog on one name, then feed over to zasurvivalstore for all sorts of survivalism and zombie related merchandise, feed over to zasurvivalgear for more specifically-targetted stuff that sounds like "gear", etc. (more work, but might be worth it).
One thing I think you may run into, or may want to research and think about a bit, is that you are actually targetting two niches - people who find zombies amusing/interesting/bizarre (and aren't that serious themselves about zombie threats) and survivalists - people who really believe that the Mayan calendar is right, or the New World Order is about to get them, or the big War is about to get started and they need to lay in a supply of 30 years worth of food and water in their bomb shelter. Survivalists take this stuff really seriously. Some of them will be put off by talk of zombies. And zombie fans don't really take their stuff so seriously. So you might want to think about actually dividing the two niches in terms of strategy.