The best defense would be to be invisible. However, if a majority of a population survives a disaster, there is little to no space to disappear to. After a few weeks , people less prepared would start roving. There are few areas other than wilderness where you could truly hide.
We can leverage our success in a disaster in a number of ways...but the best way to survive in a SHTF situation is not to get in one to begin with.
I have no idea how to avoid that situation though...