A bandolier was an article of clothing.
Kahler-Tek wore a bandolier to carry ammunition. (TV: A Town Called Mercy)
The War Doctor wore one, taking it from Cass's body shortly after his eighth regeneration. (TV: The Night of the Doctor) He wore it until the end of his life. (TV: The Day of the Doctor)
At some point before Cass’ death, the Thirteenth Doctor met Cass and gave her a bandolier. (PROSE: The Day of the Doctor)