Carradice Carradura Midi Saddlepack - Black/Grey - 0.9 Litre

I recommend this product

Running tubes on 50mm tyres means you need plenty of space for a spare tube. This saddle bag is just right. Enough space for multitool, two spare tubes for 50mm tyres, tyre lever and the like. There is also an extender zip that gives a bit of extra space.
On to the bag itself - there are lots of trendy saddle bags out there now. This one is solid, really well made, stable and the price is excellent. I also very much appreciate the rear light loop as, if you are small like me, there is not room on the saddle post for saddlebag and a light underneath. If you have a rear light that can be fixed to a loop this saddlebag is the best.