Who doesn't have old USB drives lying around just waiting for something interesting to do? Fortunately, a USB drive can make a great identification device should your dog ever get lost.
We've talked about allkinds of cleveruses for USB drives. Instructables user ctx1985 shows us another-one that just might get your lost dog returned to you. The idea is pretty simple. Place identification and contact information about your dog into an easily accessible file (a plain text file should work fine). Put that onto an old USB drive and then attach the drive to the dog's collar. You'll probably want to use a somewhat weatherproof drive or maybe wrap it up with a bit of duct tape.
As for the contact information, that's up to you how much you're comfortable putting on the drive. At the very least, it should contain the dog's name, breed, and general appearance, as well as your phone number or work number. Other things you might consider including:
Any allergies or medical conditions your dog might have