The first and foremost tip to do before taking an examination is to have a good night sleep a night before the actual day of your test. And avoid waking up late so that you will have a time to take a shower and to eat a breakfast. Your breakfast choice should not be heavy because you do not want to be disturbed by “call of nature” during your test.
I recommend eating the usual breakfast that you are used to eat or something like oatmeal and a banana or a sandwich and a cup of your usual morning beverage. Of course, after your normal morning routines, you should now check the things that you need to bring on your exam like extra pen, paper and calculator (if allowed).
And unless you have several extra hours to spend reading before the exam schedule, refrain from bringing books and other reading materials. Instead, take time to relax so that you can be more productive during the actual exam.