Right now, I am more worried about a government mandated "bank holiday." If Obama can't convince the Saudis to continue to price oil in dollars, we may have a problem. The Chinese International Payment system is being coordinated with the European SWIFT system. That will pretty much eliminate the dollar as a reserve currency.
If the Chinese back their currency with gold, the dollar is a dead duck. There are about three or four times the amount of dollars being held overseas than that in the US. When all of those dollars come back to the US, we will have a terrible inflation. Remember the Carter administration, high inflation and high unemployment. Well, this would be worse.
Keep cash on hand, and I mean fives and tens. When none of the cards work and the teller machines are tuned off, you will need cash. And not many people are going to be able to break hundred dollar bills.