Almost anyone can tell you what you need to buy TODAY to prepare yourself for a civilization-ending disaster, like, of course, the zombie apocalypse. That's easy.
Survival gear. Lots of it. Maybe an underground bunker, too.
Except that you need to be near your gear and get to your bunker when the dead rise up. All of that stuff is less useful if you're somewhere other than your bunker when things fall apart. Plus, what if you're not prepared for the right kind of zombie apocalypse (or any other sort)?
What's more useful is knowing how to shop AFTER the the zombie hordes start rampaging.
Personally, I do not expect the dead to rise, but as a fan of science fiction I'm well versed in apocalyptic visions of the future. There are numerous ways civilization could crash and burn. Asteroids ( Lucifer's Hammer ).
As a Boy Scout I learned that being prepared wasn't trying to carry everything you need with you at all times (although I still carry a pocket knife wherever I am permitted). Being prepared is being INFORMED. It's knowing how to do things, not so much having the all of the tools to do ANYTHING with you at all times.
That's how you'll survive the end of the world. Knowing what to do, not having a lot of stuff stacked in your closet.
You could have your "go-bag" ready, but what if you're no where near your go bag when the shit hits the fan?
So relax. Get out of your cold, dark, bunker and enjoy the sunshine while you still can. The apocalypse isn't the end of the world. It's just an opportunity to go shopping!