I can't see doing it without a drop bag at Loudiac. Well, I can, but it would be unpleasant. The spirit of PBP includes local clubs renting campers so their riders can avoid the dorms and cafeterias, the Europeans and particularly the French go whole-hog on individual support. You will see riders on PBP that look like they are on a tour, that's often because they rode halfway across Europe to get there and brought everything with them on the ride. Most people are much better supported than that, at least a drop bag or bags.
The main thing I would pack if I was to go without a drop bag is 4 pairs of bibs. I like to have spares. Not sure what else you really need.