In all seriousness, you just can't be prepared for an unexpected event. I find that survival "preppers" are preparing for a very specific types of apocalypses. They may be out of luck if things turn out differently than they expect.
You could prepare or buy a "go-bag," like one of these (not a bad idea), but in all likelihood you will be far from the bag when the shit hits the fan.
And if nothing at all happens, which is the most likely thing, then they've wasted a LOT of money and time. It's a very expensive hobby.
But you can be prepared by being flexible and informed. Don't worry about stocking up, just know how to get what you might need. And how do you know what you might need? By using your head, by thinking, and being aware of the bounty of things around you that really can help you to survive.
I hope that this guide has helped you to think about the non-standard places to look for and find all of the stuff that will help you live on. That's a useful skill in pre-apocolyptic times.
Plus, shopping can be fun!
My challenge to you is this: think of all of the places where the fleeing mob will never think to look for the things that they'll need.
That's where you'll find me.