As far as I know there is no way that you can limit the ability of the phone to edit content.  That said there are many steps you can take to ensure that somebody won't be able to get to the stage where they can delete your content and dealing with it if it happens:

 - setup a pin number on your sim
 - setup a lock screen on your phone
 - install an application like [SeekDroid][1] and give it admin access so that you can remote wipe your phone if you lose it
 - install two factor authentication on all accounts which support it (Google, Dropbox, Facebook certainly do atm.  Others may)
 - make regular backups of anything you would be lost without, and store those backups in the cloud or in multiple places
 - don't use the same password more than once.  I use [LastPass][2] to ensure that all my passwords are all over 20 random characters.

You should really follow all of these steps - it adds a bit of overhead to some tasks, but I certainly favour the security over the convenience. 


  [1]: https://play.google.com/store/apps/details?id=org.gtmedia.seekdroid
  [2]: https://lastpass.com/