brain endurance booster for test day advice needed

I'm an afternoon tester, which allows me to eat lunch before the test. I've never been much of a morning person, and I find that my energy level is highest in the early afternoons.

I'm also in California, so my pre-GMAT meal of choice is usually an In-N-Out Hamburger, "Animal Style" with extra pickles. As HanoiGMATtutor already mentioned, it's just enough to give me energy throughout the test, but I skip the cheese to avoid that too-full, tired feeling that you get after a heavy meal, which can slow down your thinking and make you feel drowsy. Then, I'll also bring a Cliff Bar (Oatmeal Raisin Walnut) to the test, to nibble on during the breaks, if necessary...but you really won't have much time to eat since the breaks are only 8 minutes long. (You will have to store any food and drink in your locker before the test begins.)

https://www.mba.com/us/frequently-asked- ... enter.aspx

Optional: 5-hour energy, legally prescribed ADHD medication, etc.

If you're completely drained after the Quant, then maybe the issue is that you're expending too much issue on the AWA / IR sections. Remember that those sections of the test are not as important as the final two sections, so try to conserve some energy during these first 2 sections of the test.

Or, maybe the issue is that you haven't taken enough full GMAT practice tests. Test-taking endurance is a skill that must be practiced in order to maintain it.