If you're ever in an accident or have a medical emergency it is important for authorities to have an easily-accessed emergency contact number so your love ones can be reached. Given that many of us lock our phones, you may want to consider editing your lock screen wallpaper image to include an emergency contact number.
As you can see with my example above, even if you can't get into my phone's data you still have an emergency number listed. My phone's locks screen wallpaper is the excellent R2D2/Iron Man mashup by artist Mike Verta available at TheForce.net.
Another popular idea in this area is to list a number in your contacts under 'ICE' (an acronym for 'In Case Of Emergency'). However, that's only useful if your phone isn't secured with a password -- and given the huge amount of personal data on most smartphones, having additional security is definitely sensible.
Top Tips for Securing Your Smartphone [Ghacks.net]