Too Many Credit Cards
Don't carry every credit card you have: If your wallet is lost or stolen, the thief will have a field day with more cards to rack up (leaving you more headache to deal with). Plus, you won't have anything to use in the meantime as you take care of getting new cards. Carry only one or two of your main cards, and possibly a backup, and leave the rest in a safe place at home.
Extra tip: Keep photocopies of the fronts and backs of all your cards at home. If your cards are lost or stolen, you won't have to hunt around for numbers. Also, never close your accounts—ask for your account number to be changed. Closing an account can damage your credit, and you may lose previous reward points, interest rates or credit limits.