The Order backpack collection items that are rewards for completing story chapters seem to be only receivable by the first character to choose that backpack.
When completing Prisoners of the Dragon, I chose the Recruit’s pack on a mesmer and then later again on an elementalist, then continued the story past Prized Possessions with the elementalist first. Progressing the elementalist through Strange Observations and Buried Insight did not grant the buckle or the padding, but progressing the mesmer afterwards granted both.