Lots of fluid and lots of snacks for the day... stay hydrated. When you feel your eyes starting to shut on their own, get up and go for a walk, chat with an instructor, then come back and start again.
Stick with it, and you should be able to get through the prep at least 1 and a half times. Take some time out to study the formula's. They may have an "example" sheet you can study from. If you have the formula's down, then you won't have to worry about the memorizing those questions because they just become "plug & play" with the formulas.
I don't normally drink soda's, but Dr. Pepper and a large bag of peanut M&M's got me through the prep.
Good luck!