I almost always ride solo and have a Road ID on my left ankle, (hate 'stuff' on my arms/fingers). They had a special on colored bands awhile back, so I'll ride with a contrasting color to whatever kit I'm using that day, (usually either red or black). I do not carry my wallet, but do carry about $30 in a little baggie with a slip of paper with emergency contact info. Here is what is on my Road ID:

First Middle Last / 1951
Palmdale, CA USA
Jane 800-555-1212 Friend
Jim 800-555-1234 Brother
Kaiser #7240000 - NKA
Diabetic T2 - O Pos Blood

That should have everything important when they find my crumpled body laying along the side of the road. Health insurance info, No Known Allergies, blood type, age, diabetic desig., and contact info. "USA" because of riding in foreign countries.