You need to be careful with these: packed incorrectly, batteries can melt and do serious damage to your luggage—and your camera equipment.
There are two main choices with batteries: rechargeable, and non rechargeable. While some cameras don't give you any choice on the matter, others allow you to use standard AAs or other types, rechargeable or no. But for travel, which is better, rechargeable or non rechargeable?
Rechargeable. It's cheaper over the longterm, which is nice, and it saves you the hassle while traveling of trying to purchase new batteries whenever you run out, which are often more expensive in tourist destinations. A charger isn't adding too much to your luggage, so it's an A+ on all sides.
Make sure that you store your batteries and battery charger in a cool, dry place away from direct sunlight or temperature changes when not in use. You may need an adapter for the outlets if you're traveling out of the country, so purchasing that ahead of time is definitely an advantage.
It definitely pays to keep an extra set of charged batteries on your person at all times, just in case the camera runs out and there's that perfect shot...
There are a number of things you can do to increase the lifespan of your batteries. For more information, check out this article on battery care.