The thing is that you can't - securing yourself financially assumes that the society around your will be stable enough for the things you have secured (money, any other assets) to remain valuable and safe, which they won't be if you have huge societal disruptions and the majority of people are unemployable.

To oversimplify it - you'll either be breaking someone's window for food, or you'll be the one having their window broken. Chilling out and withdrawing a stable 4% out of your stock portfolio won't be an option.