Never leave home without it. Not American Express. I mean your business card. Actually, bring LOTS. Not every traveler realizes how useful they are.
Make sure you hand your cards to everyone you meet on a business trip.
Your cards should have your traveling number printed, as well as the number of your home office, and the email you actually check from the road. This will be invaluable to you for keeping in touch with people you meet along the way, as well as establishing your creditials in innumerable and frequently needful situations.
Take along a nice stack - depending on the length of your trip, you might bring a hundred cards in your luggage. That really isn't too many to bring. Just make sure you hand the right cards to the right people, if you, like me, have multiples - cards for your main business, side business and hobbies.
Have several dozen on hand in your laptop case or mobile device bag. This way you can pass them out to anyone you meet - or better yet - slip along two or three (to pass along to their friends, co-workers, etc).
Always gladly accept business cards from other people you meet. The corporate world perks along on networking. Offer yours in return, when gifted with one yourself. It is only courteous.
In some cultures, handing out a business card is even considered more proper than shaking hands, and much more appreciated. It's good to do a little investigating before you head out. Ask your boss or co-workers how people use their business cards in different countries they head to.