Photos and Videos: Use Google Photos on Android or iPhone.
Turn on Backup & Sync.
Set up Google Photos
iPhone users can also use iCloud Photos via Settings > Photos.
Contacts: iPhone: Sync via iCloud. Confirm under Settings > [Your Name] > iCloud > Contacts.
Android: Ensure Google sync is enabled in the Contacts app > Settings > Sync accounts.
Messages: iPhone: iMessages are included in iCloud backup.
Android: SMS backed up through Google One. For advanced control, use SMS Backup & Restore from the Play Store.
WhatsApp Chat Backup
Android: Go to Settings > Chats > Chat Backup and link to Google Drive.
iPhone: Use iCloud Drive for WhatsApp under Settings > Chats > Chat Backup.
Documents & Files: Use apps like Google Drive, Dropbox, or Microsoft OneDrive to upload and access files from any device.