I carry spare tubes, levers, multitool, and 2- CO2 cartridges in mine. It can fit in a jersey pocket, but it can get heavy for a jersey pocket if you load it up with CO2 like I do. I prefer to pop it into my frame bag and it keeps it all from floating around and getting lost. This also makes it easy to hope on a different bike. I can just grab this bag and know I have what I need for minor roadside repairs.