The best android wallet app has built-in easy backup system which also encrypts your backup file with a password onto a memory-card.

As long as you make sure to use that backup feature often and keep several copies of the backup-file on several disks/CDs etc it won't matter if your phone dies.

Just make sure you make a new backup every time you create a new receive/secret key in the wallet app and you should be as safe as it can be. And don't rely on just keeping ONE copy on ONE disk. Be sure to spread it onto several USB sticks/disks and maybe even burn a CD backup to ensure you are secure from major disasters.

Much better than using any online wallet I would say.