Everything you can carry in it!!!
- Familiarity: I've put it through the wringer
I have the medium one and I carry 2 CO2 cartridges along with Genuine Innovation Microinflate Nano, 2 tire levers, chain tool, Park Tool folding allen set and some spare change. I was looking to upgrade to the large, but I really don't know, I really want to keep it simple under the saddle. After muddy rides it's really simple to clean and dry fast.