1. A good spot (well duh)
2. Good skier(s) (no shit)
3. A camera (DSLR recommended), and a good filmer... these are both optional of course, but your friends are gonna think its a claim if you don't have proof, so bring the camera anyway.
4. A photographer... obviously it could be the same person who is filming, but for anyone really serious about getting shots and pictures...it may be a good idea to have a filmer and a photographer.
5. (Now the real supplies) A shovel, in fact bring a few.
6. Salt, don't want that kicker to collapse on the approach.
7. LIGHT, a shot isn't going to look too good without enough light to see. Those parking lot lamps do not do the trick, bring a flood light or two.
8. Water, you'll thank me later for this one.
9. Red bull/Monster/etc. If you're getting a shot out past your bedtime, you may want some energy.
10. Bungee; A lot of urban spots are not going to have lots of run in space to get speed without one and bringing that one friend along just to pull you the whole time doesn't blow over well either.
11. Granola bar/snack; if you're an amateur like Steve Stepp ;) then its probably going to take a while to get a good shot, bring some food.
I am probably missing some key items so feel free to add whatever you think is something important to bring to an urban session.