Pat recently did a "What If.." article where he asked, amongst other things, "What part of your art is most rapidly teachable and imminently functional?"
In the post apocalyptic future of the damned that Pat set forth in his scenario i chose to teach the survivors the aiki brush off. I like it as a intro to aikido because it basically covers (in my mind) may of the things that make aikido aikido:
1) it's a decent intro to the concepts of ma'ai
2) it helps learners pick up on the lines of attack
3) (i think) it's an easy way to show people just how little force you need to deflect almost any attack
4) anything else i may not have mentioned
The time's we used it in class, during the seminars about knife defense, and at at Sensei Charles' dojo against various forms of faster forward attacks i've gotten to be something of a fan of it.
I agree with Pat that it won't really stop any conflicts but versus most types of the slow moving undead and those radioactive mutants with a low movement rate it WILL allow a holocaust survivor to wade throw small to moderate sized groups of them without much trouble. Throw the brush off in with almost any ones basic tools of punching and kicking and it's a good place to start. Another thing that might help would be the ideas behind "rolling the ball" and i'd be satisfied for group forays into the shattered wastelands to forage until they could train more.