There are commercial vendors that supply wallet cards and wearable medical alert devices that display just your primary medical condition, like "Diabetic," or whatever else you'd like, including I suppose nothing, along with your unique patient identifier and a telephone number and/or website that can be contacted for additional information. That's pretty secure. A flash drive with your medical information on it can also be useful, but probably not as useful in the early part of a medical emergency.

The best place to wear a medical alert device is on the left wrist, IMHO, primarily because most American ambulance designs usually cause the medic to work on a patient from the patient's left side, and an ID is therefore more likely to be spotted while taking a BP, starting an IV, etc.

If you don't want to deal with a commercial vendor, I don't think it would be too hard to set up a reasonably secure, password protected website with your medical information on it, and to print up your own medical alert card with whatever you want on it, including your website password. Then, if your wallet is lost or stolen, you could just lock out your website. Alternately, you could just give the password to those listed on your wallet card as emergency contacts.

My DMAT team created accountability tags that allowed members to print out their medical information confidentially, and include it inside wallet card sized ID card/slipcover, which was then laminated closed and sealed. In an emergency, the card could be cut open along the edge and the medical information slip removed.