If you have your bank withdrawl receipt on you, you can walk around with any amount you want. This shows that you haven’t been concealing the cash from anyone and that you did allow the government an opportunity to freeze it if they chose to do so.
Be sure to have a tracable stream back to where the money came from, ie. regular bank deposits, sale of stocks or a home or something with a serial number on it, automobile, airplane, gun collection, etc.
Uncle Sam gets real nervous when people do things that aren’t in the norm. Making money and not paying taxes on it gets him all upset. Bartering is considered criminal these days if you don’t pay all the taxes they think are due.
So what's the cutoff amount... can they seize "undocumented" cash amounts over $20K, $5K, $1K, $100?
Does the law that provides for this index the limit for inflation?