Two things that are a MUST:
1) a WATCH (timer)
Your watch might not have the same hour with the proctor, so you should write down your stop time. You could speed up or fill a blank at the last five minutes.
2) a bottle of water (I like a COKE)
*** If you run out of time, what do you do?
You should choose ONLY one letter for all remaining unanswers. As doing so, you could get AT LEAST 25% correct!!! One educated guess in choosing that ONE letter: look at the OVERALL of your scantron, then choose ONE letter that could do the balance of those answered dots on your scantron. The exam preparer wants to distribute evenly all answered letters!
And you are lucky to have friends at SDN to share your thoughts, so you have much confidence. Good luck!