10 day trip to Barcelona

Some countries requires that your passport has at least 6 months validity left.

Make sure that your luggage has a tag with your name, address, and telephone number. Tie a colorful ribbon or attach distinctive stickers to your luggage so that you can identify it easily, and other travelers will not take it by mistake at a busy terminal.

Remember to keep a close eye on the passport copy - it's a great asset if you lose the original, but can also be used to steal your identity if it gets into the wrong hands.
If you have a web based e-mail platform, e-mailing yourself scans/copies of important documents and passport info is a great alternative to hard-copies. It's easier to access, less likely to be stolen, and guaranteed to always be on hand.

In case all your money, or all your gear, is lost or stolen.

Memorize PIN codes to credit cards so that you can use them with ATM machines to get cash.

Where pickpockets are a problem, carry your wallet in your front trousers pocket.

Use ziplock plastic bags for any items that could leak or possibly break in transit.

Take a pair with pockets - doubles as a swimsuit for men.

Keeps your ears warm and works as a sleeping mask as well.

Easily stolen, so don't bring anything too valuable.

Ask your doctor to provide you with a letter for any prescription medications that you are taking with you. Keep medicine in original containers, if possible.

For international travel: consider unlocking your cell phone SIM card so you can use your phone there (purchase a local SIM in your destination).