A dry waxed canvas bag made by VO, with leather straps.
The straps are spaced to allow it to hang on either end of your bike. It's big enough for a mini-pump, rain shell, tools, tubes, a banana, a wallet, and even a camera. Access is via a full-length zip. It's about 30cm x 11 cm.
This new version has a third strap that can be attached to your stem or seat post to limit swaying. A light can be clipped to the name strap.
If mounting on top tube, we suggest securing one end to either the head tube or seat tube.