Be sure to try all of the equipment at least 1 day before the event. 

Charge all of the batteries; clean each lens; check that each flash card is
formatted, empty, and can record a test image. 

Don't forget to bring lens cleaning supplies, brush, and canned air as well as
rechargers with an extension cord/power strip.  Having an inverter (12v DC to
115v AC) would allow recharge in the car.  Having a fully charged cellphone
and list of contact numbers wouldn't hurt either.  Small notebook, pen and
business cards ...

Last but not least, bring a sense of humor. 

--
Martin

p.s. They say that duct tape is the force that holds some events together
... and it has both a light and a dark side.