The best advise (it's also applicable to the Compartment course) hot shower. On the BA course, just prior to tea on Saturday - have a shower - it aids in relieving the body and makes Sunday a little easier. The other - drink, drink and drink - H2O of course and be relaxed.
As for eating - thats up to individuals, the
story of heaving in your mask has been around now for 10 - 15 years - it has happened but when it did it was due to other reasons - drinking to much the night before and pre existing illness.
SO - enjoy it - thousands have done it before you, so it's safe, fun and a real eye opener - have no preconceived ideas and an open mind and you will come away full of new, exciting and wonderful knowledge - the instructors are first class, facilities first class and and you come away with a skill that is fantastic