I wanted to second everything @Bravo721 said and emphasize that if you can't control your anxiety you might blow it. They really go way out of their way to make this comfortable, I honestly can't think of anything they can do more or better, so if with all the effort they put into this you still can't relax, keep your cool, how are you going to handle way more stressful situations in a clinical setting? Side note: relaxed doesn't mean loose. Emory was my third interview so I have a bit of experience.
You will do about one hour tour of the medical side of the campus. When they say wear comfortable shoes, they mean it. Ladies, if you have reservations about ditching those heels (I did), don't. I believe everyone on my interview day wore flats. Period. Also, I know this is October, but Emory is in Georgia. It's still hot and humid. If you come from somewhere up north it's going to hit you like a train. Luckily the tour is after your interview. We all ditched our jackets before we went on the tour. Just keep that in mind and don't stress about it.
Don't stress about the writing (boy, was I stressed about the writing!). The prompt is rather broad and gives you a lot of leeway to come up with something. Even if they change the prompt from one interview day to another, I imagine they keep the same format. Just make sure you are coherent in your exposition. That's really what they are looking for. We all took the GRE and had to write an essay on the spot, right?! This one is easier.
The last tip I would add is to pay attention during the group interview to everyone and everything.
Good luck y'all!