With the limited time before the event... don't make any major changes. Changing the brake fluid is a good thing or at least bleeding it before the event.
Just make sure your car passes a tech inspection and everything is secure and safe.
Going to the event, bring spare fluids, a tire pressure gauge, and and air pump if your pressures are low. Monitor your car's health between sessions by making sure you aren't leaking any fluids, check your tire pressures haven't gotten too high, and make sure you aren't rolling over your tires too much in the front (you'll see wear on the sidewall if this happens).