This is simply and blatantly not true. A citizen, in fact, can possess, quite legally, cocaine, which is a Schedule II drug under the Controlled Substances Act. In your state or any other. Many people are legally authorized to obtain and possess cocaine in your state. Unless, of course you live in Kazakhstan, which from your understanding of the government's role and your role within that may be possible.

Concerning cash, and your post, here:
This is highly inaccurate. Where my cash goes or does not go is none of the business of the federal government. It has no right to track cash that I or anyone else spends or hides away, once I have paid taxes due on earnings. The only government interest in my cash is: Did I pay the appropriate tax on any income that I made? If the answer is yes, the government's interest in my cash ends. Whether I spend it on peanut butter or rare diamonds. The government may like to know where my cash came from but it is none of its business, as long as it was properly declared and I have paid the appropriate income tax on it.

Al Capone wasn't busted for running rum and tobacco. He was busted for not declaring and paying income tax on his earnings. Had he declared his earnings, he would not have gone to jail.

I hope I am the one you "catch" with $20k in cash on a trip. When you do and you detain me, I shall use some or all of that cash to ensure that you get your chance to use your logic to explain to a judge why you overstepped your administrative authority....oh wait! The ACLU has already given you that opportunity.