Zion is one of the most beautiful places on earth. However, one thing to keep in mind, is that there is no car traffic allowed in the park - you will have to take the shuttle bus to get into the park. Get a good comfortable backpack for your food, water and cameras. If you are planning to hike the narrows, you will get plenty of opportunities to drop your things into the river. For that particular hike I'd recommend a camera that will not start sparking underwater, or at least you won't feel too bad if it gets splashed along the way ;-). A water-proof bag with easy access to the camera would be very helpful there.
Most of the things in Zion are some hike away. Think about what you are willing to carry for a few miles with large elevation gain.
Have fun, you'll love the place!