If your wallet is ever lost or stolen, you need to immediately contact the issuers of all the credit cards and identity documents and begin the process of getting new cards.
About once a year, lay out the contents of your wallet on a photocopier. Copy both the front and back so you have a record of all the card numbers and phone numbers.
Be sure to keep the copy in a very safe place. When you make a new sheet, be sure to shred the old one so it can not be misused.
File a police report immediately in the jurisdiction where your credit cards or wallet were stolen. Do not wait until you return home. Promptly calling the police shows to the credit providers that you were diligent and will be the first step toward their investigation.
Consider calling the three national credit-reporting agencies to place a fraud alert on your name and social security number. That will make it a bit harder for the thief to open new accounts in your name.
If you are traveling, keep your identity document (passport or drivers license) separate from your wallet. You should also carry a photocopy of the first two pages of your passport in a third pocket whenever traveling abroad.