Here are the supplies you'll need:
1. Plain sheet of thin magnetic material. I found one at a local craft store for $4.
2. Sheet of clear single-sided laminate - office supply stores carry these.
3. Spray adhesive
4. IDs - you can find templates for free online. There are several out there. I used this one: http://dogandcatid.com but I may try to make my own as this one turned my high-res photos to pretty low-res when I printed it.
As for instructions - just spray the adhesive onto the magnetic sheet, place on the paper IDs and cover with a clear sheet of laminate. Pretty simple and cheap. I like that I'll be able to store the IDs I'm not using inside the little metal flap on the Variocage doors.
As for tips on what to put on the emergency ID cards - I will always warn that my dogs may be frightened in case of accident, Nari hates other dogs so I put that on her ID, I also guarantee vet costs/reward and never put the microchip number. That number is something I don't make public as it's something that helps me to prove I'm they're caretaker.
I also have this magnet on my bumper that I got from a fundraiser.