Pray for your doctor, surgeon assistants and nurses, that they may be perfectly aligned with your procedure that day.

DO look into holistic pre-surgery advice, though no doubt they have provided you all you need to know. Here's one:

What should I eat the day before brain surgery?

It is recommended to maintain a clear liquid diet the day before the surgery, here are some of the liquids allowed:
Water.
Clear broths (chicken or beef)
Juices (apple or cider)
White grape juice.
Tea (with no milk or honey)
Coffee (no milk or creamer)
Jell-O (without fruit/no red Jell-O) - - - [wow, no RED jello?]
Popsicles (without fruit/cream)

If it's all about liquids, throw some baking soda in water first thing and alkalinize, or at least lemon in juice water. Prep your body for its magnificent healing event.