bathoutdoors.co.uk has used the Blackburn Outpost Bikepacking bags for years now and believe they are one the best systems for people getting into bikepacking.
Blackburn says - Keys, check. wallet, check. energy bars, check. hydration bladder, check. The Outpost frame bag is the perfect companion for your all day pleasure ride or your week-long adventure ride. An expandable bottom compartment accommodates more mission critical gear.
This Small size is perfect for bikes 15" to 16" or 52cm to 54cm. if in doubt please contact the store for advice.
• Expands to fit a wide variety of frames and sizes
• Simple to install and remove
• Highly water resistant
• Interior organization and exterior slip pockets
• Includes hydration tube port