I think you've pretty much hit the nail on the head there: in any disaster scenario, it's the Military that makes the rules and decisions about who goes where, when, why and how.

Generally speaking, your chances of survival in such a scenario are higher, if you're an army grunt ... and, therefore, (because you will stand at the gate and shoot people to order) of more use to the Generals ... than if you're a billionaire (who will attempt to throw your weight about because "don't they know who you are?").

The Military elite doesn't need money (or any other form of wealth) in order to wield power ... there's a chain of command that those lower down obey without question rather than get shot for disobeying orders — in an 'end of the World' scenario, billionaires will quickly find they are no higher up the scale than the boy who cleans their pool.