I've got great advice on this one.
DON'T DRINK ANYTHING BEFORE THE TEST.
You show up before 8:30, but you won't begin taking your test until about 9:30, or later if you have bad proctors. You are not allowed to leave the room after you are "officially" checked in (which is when they hand out the testbooklet. You can, however, leave the room once any of the tests have begun (but this cuts into test time). I actually left during the reading comp (i usually have 3 or 4 minutes left in that section) because I was dumb enough to drink two cups of coffee about an hour before the test.
This translates to no sanctioned bathroom breaks from 8:30 to about 11:00. This time consists of filling out the test, and then taking the first 3 35 minute sections. There are no sanctioned breaks during that time.
Regarding cell phones, pagers, mp3 players, etc. Don't bring them into the room. Assume that you will have the worst/meanest proctors in the world.
Bring a silent timer, a bunch of pencils, and a good eraser (not the ones at the end of the pencils).
btw, I got away with having one bottle of water so that I could have a sip or two to clear the dry, nervous throat.
hope this helps.