The idea of caches is a good one. Unfortunately, for the time scale on which disasters where you might use it is concerned, I think the obstacles are too big. The only exception might be hurricane evacuation, but even there you have some major problems. A big one is simply that a lot of things you might want to store, fuel, lamp oil, etc. Are usually against a storage company's rules. They don't want a fire or explosion on their property. This is the problem I think caches have for hurricane evacuations. You can't store fuel for your car. Likewise, if a place is accessible it probably isn't climate controlled, which means food, even MRE's have to be replaced every year or so. And again many places don't want you storing food there anyway.

So outside of food or fuel what would you store? Camping supplies? Maybe, but if you saved the $50 (minimum) a month rental fee, in a year you could afford $600 to buy or bribe you're way into a hotel or motel for a night. Cold hard cash might be a better survival tool then what you'd store, even if you have to be price gouged a little.

Finally, problems of security versus accessibility come up. If you can get into a place when the power is out, you're stuff will probably be gone pretty quick. If you can leave it for a year or two unmolested, you probably can't get to it in an emergency.