the.com/saddlebag

means A pair of joined pouches slung over a horse, bicycle, or motorcycle's back to carry gear on either side.

from Straightforward compound of 'saddle' (from Old English 'sadol,' going back to an ancient root meaning 'to sit') and 'bag' (from Old Norse 'baggi'). The device itself predates the word for it by centuries — riders have been draping pouches over saddles since antiquity — but English simply welded the two plain nouns together once the thing needed a name.