I found a camera bag that will carry all my lenses (but I will probably only cart around 1 lens), memory cards, & batteries in a bottom, water resistant section, and has room up top to be a small backpack. Even has little nets on the sides for water bottles. I found it at Circuit City, but I have seen others like it around.
One bit of warning: Do not, under any circumstances pack a digital camera in your checked luggage. Something about the screening process can fry the camera. A friend of mine learned that one the hard way.