Henri Cartier-Bresson used to fill his cassettes directly from a bulk roll, according to this recollection of his time in India:

http://www.r3maf.com/Ishu_Patel_HCB.html

Of course, he probably had a couple of decades of practice. I do like the idea of pulling the exposed film out of the cassettes and wrapping it around a core, instead of carrying lots of exposed cassettes.