Leo says a thumbdrive will work, and Sandisk makes secure thumbdrives that encrypts anything in a protected folder with 128bit AES. Additionally, Sandisk offers 2GB of secure access in the cloud.
There's a medical USB key from Medic Tag. RoadID.com is another good option. Similar to Medic Alert, it contains information that authorities could use to access his data in the event that he can't give it to them himself.
The real problem is what happens if he's unconscious and the doctors or authorities don't have access to his password. It's certainly a conundrum to create a device that is secure, but able to be accessed by a third party in the event of an emergency. Doctor Mom in the chatroom says to have a card in his wallet, or a medic alert bracelet is the best option for medical information since time is a big factor in the emergency room.