If you're ever in an accident, the one thing that should be on your person is your iPhone. Just make sure it contains your medical details. iOS8 has a new feature that lets you set up easy access to your emergency contact info and medical ID without having to unlock your iPhone.
With iOS8, Apple also released the Health app. So go ahead and open that and go to Medical ID tab in the navigation. Here you can enter your medical information along with emergency contact information. Add in your name, your birth date, any medical conditions, allergies or medications you might be on, as well as blood type and other details such as your height and weight. Add as many emergency contacts as you please also. At the top, be sure to have "Show When Locked" switched to on. This will ensure that this information is available to paramedics without them having to unlock your phone.
To access this information from the lock screen, swipe right from the lock screen and tap "Emergency" from the bottom right and again Medical ID. Voila!