Pragmatically, there's not much to worry about if you are just buying coffee.  If you convert large amounts of bitcoin between fiat, then you would have to document this on your tax returns to match what your bank is reporting to the IRS.   i.e. you buy a 1 btc now at $600 then sell it later for $1200.   If you spend bitcoins in commerce, the merchant isn't required to report to the IRS unless it's over $600 a year.   It may be a hassle to comply with the law, but I suspect you might have a computer to help you with that.