definitely check all your fluid levels and tire pressure, generally run ~34-36 psi cold but that will vary greatly depending on numerous factors. take a torque wrench and lug socket if you have one and check your lugs before each session (~95 will do it), if you don't have one either buy one or you will likely be able to borrow one. don't forget your helmet, if you're not renting.
question: are your coils on softest for street comfort? I assume so, for the track you will definitely see an improvement in handling if you firm them up.
overall have fun and be safe your first time out, don't go too crazy, remember you want to drive your car home at the end of the day. first track day is always a great experience, you won't forget it.
the organization running the track day will have inspection forms for you, likely available online esp if it is a self-tech event, PM me if you want me to send you one for advance prep
2012 335is | AW on Black | 6MT | 19" 313M | Cobb AP e85 | cp-e 3" DPs | TCK Koni SA | Swift | CG Camber | CF Perf Lip | Recaro | APEX ARC-8