I think having cash on hand is always a prudent measure. Maybe even split over at least two secure locations. Even something as simple as a backhoe cutting through a major fiber optic line or some fallen tree that blacks out a large area could block access to ATM's or credit card transactions, even during normal times, requiring cash to get things done.

In addition, having direct deposit, setting up automatic debiting of important bills, like your mortgage payment, setting up online bill paying, using telephone services, using ATM's, using credit cards, etc., could very well keep you going even if the branches themselves are not open right away.

Of course, if ALL the backend stuff at your bank is compromised, then you're really in short term trouble. But even then, in cases like Katrina or Ike, the FDIC and state banking regulators asked banks to do things like cash checks from non-customers, waive ATM fees, forgive late/missed payments, loosen lending standards for short term loans, etc.

And I have my money at a local credit union, for "philosophical" reasons, as well as better rates, lower/fewer fees, and better service. Since credit unions typically share an ATM network or allow you to bank at other CU branches, I don't even need to pull my money out of my credit union, but use a closer credit union's ATM machines to do my withdrawals and deposits.