Ditto to what George said. I was allowed to take a sports bottle of juice or water into the exam. You might want to take some kind of snack bar as well. My testing center was fairly liberal on this. So you probably should contact your testing center to see what they will allow you to bring in.

You will also be intently staring at a computer screen for at least 3 hours. Whatever works for you regarding headaches is advisable also. My screen was not very big.