You assume their will be a govt as we currently know it? If things really got bad, a large portion would view the protection of their families over the country. I don't see a govt with no power getting anything from anyone. Then again, TEOTWAWKI means what I know now would be completely different.
There will always be some form of government...and they will always want their piece of your pie. What form of payment and how easy you make it for them might change in a TEOTWAWKI situation, but someone will be knocking.
No one can say with any certainty what will be currency....since TEOTWAWKI hasn't happened. Sure, situations like Ferfal's and Selco's can provide some clues, but it's still speculation.