I did okay in 2011 with a rain jacket, arm warmers, leg warmers, a base layer and a wool jersey. Except I lost my rain jacket on the way back. I might carry a wool long sleeve jersey. More than that seems excessive. There have been colder PBPs, but I don't think down to winter levels. The big potential problem is rain, because then it can be hard to stay warm. I was in the rain for a few hours in 2011, it was relatively warm. This storm came in from the east and the 84 hour riders had gotten rained on all day but most of it missed the 90h riders. We just got the tailwind