There are sites that appear to try to back Bitcoin with actual precious metal, particularly gold.  The most overt of these, Bitcoin Gold, claims to be willing to send you the actual gold which backs up your bitcoin, in the form of cubes of gold.  

There are two issues which renders this proposition a no go.  First, in addition to the standard verification to a mobile devise, the site actually demands that you upload genuine identification documentation.  We don't really know exactly who runs Bitcoin Gold but even if we did, never, ever upload official identification documentation to the internet.  Even if the owner of the Bitcoin Gold happens to be honest- which is a big if- it is always possible that a third party could steal the images, in which case they will have an exact image of your identification, with which to make a fake.  

The second issue is the shipping fee.  Bitcoin Gold represents that gold costs $35 American for one gram of gold.  If you trade in the relevant value in Bitcoin, you can receive that amount of gold in the mail.  However, the shipping cost is $25.  Obviously, this is a major loss in value.  You know it cannot possibly cost $25.00 to ship, so this cost is either Bitcoin Golds method for never having to actually prove its product to be backed by gold, or its method of cheating you on the price of gold, by massive premium wrapped into phony shipping expenses.  

Another method  of linking precious metal with bitcoin is in the form of physical crptowallets made out of metal, often in the shape of a coin, which carry the public and private address with which to redeem a certain quantity of bitcoin.  For the life of me, I cannot find one of these precious metal coin wallets for which the value of the metal, plus the value of the bitcoin, equals the total amount the seller is charging.

So, there are some other arrangements offered to online consumers, but not a one of them offers any kind of worthwhile deal.  For the near future, treat precious metal as precious metal, and bitcoin as bitcoin, and don't attempt transactions which purport to combine them.