Oooh, SO exciting!!!
I think you've got it all covered. Definitely drink lots of water today because the clear amniotic fluid will make the pictures come out better. 
With the sugar, I would advise drinking a tiny bit of juice or something and then bringing the rest of the cup with you. When I had my 17 week scan, I drank a full glass of apple juice and the baby was WILD. Almost too wild, and it was hard to get good pics because she was SO active. It took forever to get a clear gender shot. The tech kept commenting on how active she was. Oops!
So, when I had my 20 week sono, I had a few sips of apple juice and then brought the rest in a cup. I had it JUST in case the baby needed a little "boost" but as it turned out, she did great and only needed those few sips before we went to the appointment. Just a thought! 
Sending tons of OL vibes and be sure to update with pics tomorrow! Have fun! 