Hard to tell, and big difference between different locations I bet. But most places the ability to simply grow food is quite limited short term. That can get real ugly.
Dependency of import/export of course goes far beyond just food, though it may be the first real tough problem. This of course assumes import/export collapses with financial system.
Hm, I am not an expert on this. Barter as far as I know has big drawbacks. If I have a cow to give you and you have a horse to give me, one of us will likely get a bad deal.
I believe barter is what you use when you have absolutely no other choice. Any kind of money will probably be set up pretty fast locally. It gives you one standard to calculate toward