Assuming you have all your ski wear and equipment already:
Water for jump (not if the snow is already wet though, then you just let it sit for like 30mins before hitting)
Shovels
good rail/wall/feature preferably not on private property or in plain view of possible fun ruining douchebags
wax/file depending on the rail
balls to hit the damned thing
food/water for the soul
if you are hardcore and in a strict area possibly a police scanner/get away vehicle
Camera/tripod
light (if you are hitting at night)
I prefer nice earbuds or a nice loud speaker blasting wu-tang with a small crowd of children
band aids to fix your broken bones if its sketchy
enough snow for a drop in/bungee/winch/group of friends to pull you
other people
shitty skis
