I tried researching what these doors were used for but only found speculation. Does anyone know what the door was used for? (my photo)
Yes. That door is used for members of the rear crew, i.e. Conductor, Rear Brakeman or Flagman, to pick up train orders on the move. It was a safety feature, so that crew members would NOT have to "hang out" on the caboose steps to pick up train orders. It has nothing to do with "baggage". The IC was famous for these caboose models.