Back in iOS 8 Apple added the Health app to their native apps, which now works nicely with the Apple watch. To add to that like with allergy bracelets in case of emergency, you can create a medical id on your iPhone thats accessible from the lock-screen.
To create a Medical ID:
- Launch the Health App
- select the Medical ID icon to the right
- here you can edit your medical information
- you can also select whether you would like to show this when the phone is locked