Ray has shin and elbow/forearm guards that he hands out - no rental...at least it was like that for the '07 trip.
I remember being in a hoodie and running pants the first night and after about 10 minutes of riding I was down to a jersey and riding shorts - was just fine.
Fixxer and AG are correct - its chilly in the warehouse but you warm up quickly. So pack your bag with warm gear and just bring it with you.
DEFINITELY bring flat pedals. I tried my SPD's the first night and I about killed myself so first thing Saturday morning I bought some flats from Ray.
...and you'll probably want full-fingered gloves too.
my $.02