Your vacation will be memorable for all the wrong reasons if your cat runs away while you're in a strange city. To make your cat much easier to find if he does run away, make sure you've got proper identification ahead of time. Buy a secure cat collar with ID tags attached. On those IDs, write your name, address and phone number (including your cell phone number so you can be contacted on the road if someone finds your cat).
Also label your pet carrier with the same information. Add a travel pet tag that includes your contact information at your destination and your cell phone number.
Microchipping is added insurance that your pet will be returned to you if he is found. Cats can slip out of a collar, but microchips are impossible to shake because they're implanted under the skin. If your cat is found and taken to a vet or shelter, he can be identified through the chip and returned to you. When you get your cat microchipped, make sure the tag includes your most recent contact information, including your cell phone number, so you'll be easy to reach.
Even though your cat will be with you on the trip, bring along a recent photo of him. If he slips away, a photo is an easier way to identify him than a verbal or written description.