Hi, sorry not to reply sooner; I've been on vacation since Aug 21. It may be too late now, but also make sure that you eat approx. half an hour before starting - eat enough so that you don't feel hungry but not so much that you feel full. And bring food and drink with you to the test center and continue to eat on the breaks.

You want complex carbohydrates, protein, and fat. If you like it, peanut butter on whole grain toast is perfect. Don't have caffeine - drink something like fresh fruit juice with no artificial sugars in it. (NO high fructose corn syrup.)

Also, on your breaks, do a little stretching and exercise - do some jumping jacks or jog in place, etc.

(a) caffeine will not last the entire time - the test is too long, so you will crash before it's over
(b) caffeine is a diuretic (that is, it makes you have to go to the bathroom) - and you will have only 2 very short breaks over the course of the 4 hours that you're there.
(c) too much caffeine can actually impair our ability to think logically and coherently over a long period of time