Well, there's a lot you can do to fortify most any home. So whether you plan to find a home with some of the right things already in place or if you plan to renovate and upgrade, there are some things that do need to be considered in the initial property parameters ...
I personally would look for a place that is at least somewhat rural. If you need to commute to an urban location, you don't want to have to make your commute too far, for a lot of different reasons--but at least try to get beyond the suburban ring.
I'd want a little (or a lot of) acreage--with a mix of tillable, open land and wooded. High ground as well as a running surface water source on the property or nearby would be ideal.
A deep well is a big plus.
Determine what kind of neighborhood you are buying into and what if any zoning laws there are. Are there industrial properties in the vicinty? Rail lines? Pipelines?
How about crime rates? Is your neighborhood politically aligned with your own views?
I may be getting a bit picky here so I'll dial it back down.
What I know I want, regardless of where I am, is a shelter/saferoom, my own secure water source, and back-up power generation, as well as at least some room to grow food. If you can get that squared away and eventually meld into your community, getting to know your neighbors, you should be in pretty good shape.