If you don't already have ammo, and something earthshattering does happen, "whatever it may be", how do you plan on getting it. In 1 day the shelves will be cleaned out. Thus cash does you no good if it has no tangible value.
People will only trade what they have extra for what they need, like food, water, power, weapons, secure shelter etc. Cash only works in a functioning economy as a unit of measuring wealth. If there is no functioning monetary system, then ammo and things that people need, will take precedence over paper money.
I am not talking about end of days here, just a change in government or a series of banking failures, or even a horrific earthquake , hurricane, or series of tornadoes, something that might wipe out the power grid.