I took the trek in December of 2012 and had a great time. They give you a cool metal waterbottle that you carry in your vest/safety harness. Ham it up with the pictures, ask for whatever you want (they are constantly shooting). It is included! As PP mentioned, one CD for everyone (think photoshare).
One of my favorite parts was the lunch. I loved lounging with my cousin and exploring the bento box goodies. I suggest that when you arrive at the lunch spot, b-line it to whatever table floats your boat and drop off your camera/claim your spot. I loved sitting right on the edge.
Oh...I was a little evil too. I crossed the big bridge before my cousin and at the end (when she was halfway across, you go essentially one at a time), I bounced the bridge (checked with guide first). She was looking over the side, not paying attention...and then WHOAAA. It is perfectly safe.
They also offered bug spray when we started, wasn't a problem. Have fun!