Cash is the only truly anonymous method of payment. Bitcoin has a ledger that will be around forever. Eventually computer forensics will be able to use that ledger to peg transactions to IP addresses or possibly trace it straight to the user with the help of ISPs. If you really want to be anonymous when you buy online I suggest Simon Gift Cards and Debit Cards.
https://www.simon.com/giftcard/something like monero, begs to differ, cash is more prone to be falsified, but it is not the best anon option available
yeah you need to buy monero at first, but you can always mine it if you have a powerful rig, and good cheap electricity