I'll tell you what not to do.
I woke up the morning of and I had to go pee really really bad. I knew they would need a urine sample for the medical which was only two hours away, but I couldn't hold it. So, I eat my breakfast (rice krispies with a LOT of sugar on top) and now have an hour and a half to go and I know I won't be able to produce anything so I chug a liter of water as a little insurance.
Well, I get to the medical office and my plan worked! I had to pee like a racehorse so producing was not a problem. The problem came when they tested my pee. Apparently (I'm not a doctor so this is my best guess) the liter of water flushed out the massive amount of sugar that I had on my cereal so it looked to them like I had a problem with diabetes. And, it wasn't as if the sugar count (or whatever they call it) was a little higher than normal, it was way up there.
So, they sent me to get a glucouse tolerance test which I couldn't schedule till the next week because the office is closed on weekends and you have to fast for 14 some odd hours before the test. For those not familiar with the test, let me explain it to ya. Basically you walk in after having not eating for long time and they make you chug a bottle of this really thick sugar water. It didn't taste too bad cold but God help you if it isn't. Then for the next few hours they proceed to stick you and draw blood at regular intervals. My veins got raw after the first two so the last one hurt bad. Anyhow, the results came back a few days later and my blood sugar level was well within tolerances.
The lesson of the story: don't put a lot of sugar on your cereal and then chug a bunch of water if you are going to take your medical. It may cause you a week of physical and emotional pain.
Peace!
Skeezer