The Backup. Three copies, two kinds, one elsewhere.

The rule is three, two, one. Three copies of anything you cannot afford to lose, on two different kinds of storage, with one of them somewhere else entirely. A backup on the same phone is not a backup. A backup you have never restored from is a guess. Most people learn which they have on the day the device dies.

• Test a restore once. Open one photo or one document from the backup and check it works. That single test catches most silent failures.
• Worth this treatment: identity documents, certificates, property papers, insurance policies, and family photographs. Almost nothing else.