Many people don't realize that you can set up a "Medical ID" on your device if you have the health app that comes free with all iPhones. This is the app icon:
Once you open the Health app, a menu bar appears at the bottom of the screen. At the far-right of the menu bar is a "Medical ID" icon that you tap to enter any necessary emergency information.
Once on the Medical ID screen, you can fill in categories such as Medical Conditions, Blood Type, Allergies & Reactions, and Medications - anything that might help an emergency responder treat you in an urgent situation.
Once you fill out this information, you can access it even from your locked screen, as shown below.