The Manhattan 9-11 incident was too acute to generate a real residual threat. For a durable SHTF incident, I consider what happened to Tom Cruise when he lost the car in his "War of the Worlds" rendition. Arming yourself won't be so much due to predatory circumstances, though they will still be a possibility, but more of an armed response to being overwhelmed by sheer panic. Had Cruise's character been armed with something considerably more substantial, such as an armored car with HK-9s sticking out of gunports, he'd have had little trouble navigating through that crowd. He might've come into some resistance, even someone with something capable of taking out an armored car, but the odds would've been much more in his favor.