The specifics would rely on the details of the environment. But I’d say generally: non-kyc buying/selling of bitcoin.
Discussion
The only real non-KYC option is face to face cash purchases. All the rest go through KYC ramps, even Amazon vouchers.
How many people really use F2F?
I personally Whirpool every single sat I buy on Bisq. Bot accident, if asked. But the transfer of money is there, in the bank records.
I’d add using cash at ATMs. And in Canada you can use cash at post offices to buy, and of course mining, though that’s not nearly as easy and likely not as cheap.
Cash in mail is also an alternative , at least with no traces of bank transfers