This 6.5-litre bag is compact, but still roomy enough for the essentials. It'll easily swallow a puncture kit, spare tube, tools, a few snacks, your wallet and a compact camera.
The click-and-go mount is excellent, super easy to fit and very sturdy in use. Less sturdy is the backplate of the bag itself. The main structure of the bag is a U-shaped plastic sheet that runs from the back wall across the bottom to the front (a common construction), but it could do with being a bit thicker; the bag tends to sag when it's fully laden - our worry is that eventually the back will rip. There's a good quality map holder thrown in, and the bag features a front pocket, key holder and carry strap.