1) The pens aren't too bad, just make sure that they give you two of them before you walk into the testing room, and double-check to make sure that they both work. I'm pretty sure that the pad has five legal-sized (8.5 x 14 inches, roughly) pages, so you'll actually have ten surfaces, including the front and back.
2) The dry erase pad has gridlines on it, like graphing paper, so it's easy enough to draw whatever grid you want on it.
3) You're only allowed to have one dry erase pad at a time. If you run out of space, raise your hand, and they'll bring you a new one.
4) Yes, you can move the keyboard out of your way.
5) Eat snacks that have a good mix of simple and complex carbohydrates, plus a little bit of protein and fat--a balanced snack will help prevent a sugar crash. Energy bars (Clif bars, Luna bars, ThinkThin bars, etc.) usually work really well, but a lot of people seem to like bananas and nuts, for whatever reason. Just don't overdo the sugar, or else you'll risk an energy collapse partway into the section.
If you're going to experiment with caffeine, you would probably want to do that during your practice tests... so just don't do anything too wildly different on test day, and you should be fine.
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