Either walk through the water stations or squeeze the top of the cup together to limit the flow of water/powerade into your mouth. The first time I went through a water station during a 1/2 marathon, I tried to just run through it and drink normally and inhaled half the water.. I spent the next quarter mile trying to cough the water out of my lungs. Not fun!
And don't get too caught up in the excitement of race day and start out way too fast, because you'll likely burn out (unless you're crazy fast and awesome.. which maybe you are..) - If you know your average minute/mile pace, have a watch on and try to stay true to your goals so you know whether to push harder or slow down a bit!
Also, be sure to use the restrooms/porta-potties as many times as humanly possible before the race starts.
Someone who is busier than you is working out right now.
There will come a day when you can no longer do this. Today is not that day.