I have a tiny seatbag (PI) that holds one tube in a ziplock bag, (folded around and rubberbanded to protect the tube), a co2 pump, a cartridge and a couple of tire levers, and that practically disappears under my saddle. I can squeeze in 2 tubes and 2 cartidges in a pinch but then it bulges a little more.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett