Zefal Z Adventure R17 Waterproof Bicycle 7002 Saddlebag, Black-Red, 17L,

Large capacity saddle bag. The capacity can be adjusted from 8 to 17 liters, making it suitable for everything from short trips to full-scale endurance races. Comes with reflector and light attachment. It's perfect for storing large, bulky items like clothing, and it also comes with a bungee cord for expandability. It is made of waterproof material so you don't have to worry about water getting in.