Some Final Words of Wisdom
1. Stay hydrated! It can be easy to not realize how much your body is working. Between walking around all day, standing in wait for that perfect moment, and simply lugging around gear and holding up a camera (with a telephoto lens) it can really take it's toll. Carry a water bottle around with you. The Zoo might boost a ton of water fountains, but that doesn't mean they all work.
2. If you're going with company, make them/ he or she aware that you will be taking serious photographs. Don't just stop there though.. explain all that this entails: you'll be taking your time at most exhibits, and you might even be as long as 20-30 in a single spot. Trust me, they might say, "Sure, ok, whatever you want!", but that usually means they have no idea what they're in for unless they know you well enough and are used to it already.
3. Find out the zoo's policy on tripods. Most won't allow you to bring one or set it up, while others don't mind if you ask permission beforehand. There's no need for you to carry the extra weight if you can't get a chance to take advantage it in the first place.
4. Maybe bring some snacks. Food stuffs at zoo's can be simply awful, and on top of that, they can be almost offensively overpriced.
5. Just have fun. Don't get too caught up in getting perfect shots. Remember, this is just practice. Plus, you can always come back another day