Have you ever killed anything bigger than a bug? It's hard work killing things, especially a big thing that are intent on killing and eating YOU.
Forget about zombies for a moment and think about this: how would you defend yourself from a bear? The best answer, of course, is to not put your self in a situation where you have to fight a bear.
Sure, you could train yourself to be master of many forms of armed and unarmed combat. But just how long can you keep that up? It's a popular saying that a sword never runs out of ammo. That's just not true. Even the most fit, most experienced swordsman will tire and do so pretty damn quickly.
Combat hardened soldiers might be perfect for fighting zombies, but that's probably not you. You are, after all, reading a guide about zombies and shopping.
So let's forget about the zombie killing part, shall we? Let's help you survive by making you smarter and knowing where to get the stuff that you'll need.