One important tip -- get to the doctor's office on time!
If they haven't already told you, take at least a small supply of incontinence pads with you -- as you don't know how you will be regarding incontinence. After few hours you will know your likely status and then you can go shopping for more Depends or whatever. Like Sunbird, I bought a supply of products beforehand, which it turned out I didn't need.
As far as fluid intake is concerned, drink normally -- but keep your fluid intake up. If you are incontinent, I think it a mistake to restrict your fluid intake. You could argue that a small amount going out often is better exercise for those important little muscles and may be better than a larger amount less often. But try it both ways, and you be the judge of what works best for you.
Good luck for tomorrow at let's hope all goes swimmingly well