- Recent photos (of both the face and the full body)
- Personal characteristics (age, height, weight, race, scars, birthmarks, etc)
- Photos of tattoos or other permanent identifying marks
- Dental records including dental x rays
- Medical records, medical history, medical x rays
- DNA samples (most people don't have/preserve their own DNA samples which is why the DNA of next of kin are used for comparison) Here's an interesting DNA collection how-to.
- Information on personal property of the deceased (jewelry, clothing, other items known to be in the victim's possession)
Sounds kind of gruesome but for people who have experienced the loss of a loved one in a mass fatality event (natural disaster, plane crash, etc), having definitive proof that can assist in the identification of a loved one so a family can have closure is important. If you want to take preparedness to (what some would call) the extreme, consider putting together an "identification kit" for yourself and your loved ones.