In europe and Greece in particular they started using older Greek money and reset the barter points. I suspect it will be the same here.
While I doubt they will be wanting to take any FRN they will have in the back of their minds that someday when the banks get back up they will need FRN to pay their loans and such so they will take them.
I suspect that 1s 5s and 10s will be used without a problem. The 20's will be hard to cash and you will probably find yourself leaving a lot of change in the transactions.
Junk silver coins before 1964 probably will pull best trades.