You're making a few assumptions.

The largest is that there won't be massive ripples. There will be plenty of systems intact between the Rockies and the Appalachians, and the satellites will still be up, but that's the only thing I'd promise. The scenario in question involves a wall of water about 15 stories high and pretty much continent wide hitting either coast. If you just deleted pretty much everything from Boston to Brownsville and all of Florida, or from LA to Vancouver, I won't try to predict what will still works.

I would predict that that the near simultaneous destruction of that many major cities qualifies as an "almost catastrophic and far reaching event". :P I'd also hazard a guess that even though they system might work, a lot of merchants aren't going to take plastic or non-local checks about the time the news breaks.

My shopping list is easy- gas, a propane tank or two, batteries, get back to my apartment and pack up critical items. Then get my butt home before martial law is declared, which I would expect on a nationwide basis if something this large happened, and even the back roads fill with people from Mass.