What's important to remember is that in a post-apocalyptic world, we'll all be energy people, and one mass consciousness, as well as bearing telekinesis with mind-control applications, too.
(Man, I listen to too much late-night radio, even if just for fun...)
You should have a generator, non-hybrid seeds (enough for an acre,) a water purifier, a shotgun with several cases of ammunition, fuel for the generator, and... uh... I don't remember what else they say.
Anyways, when people want all that stuff, even though there won't be people, just the mass consciousness, you'd need a ray gun to do it any harm, something that fires energy, and not matter, since the mass consciousness is an energy cloud, and it could just repel, or even not be effected by anything solid you toss into it.
However, the mass conscious might not be energy, in actuality. It could be a gaseous existence. In that case, you'd want to try to turn the vapor into a gas version of a solution, or whatever it's called when you put something in a gas. Doing so, you'd dilute their thoughts, and they'd probably leave you alone.
Just saying, you know?