Noun
a large bag (or pair of bags) hung over a saddle
Source: WordNetAct 3 The other Valkyries assemble on the summit of a mountain, each with a dead hero in her saddlebag. Source: Internet
Patterson got his second roll of film from his saddlebag and filmed the tracks. Source: Internet
Small enough to fit in a "pocket" or saddlebag, they rode along on the hunt. Source: Internet