I'm always amazed at the sheer volume of crap people haul around whenever these threads come up.
I ride many thousands of miles each year with a fairly minimalist seat bag (Co2, levers, one tube, boots cut from an old tire, maybe a patch kit), and an inflator in my jersey pocket with another CO2. Cell phone, cash, credit card, ID in a baggie.
I'm currently riding some fairly deserted roads near Madrid, Spain, and I'm traveling solo. My "travel seat bag" has a whopping two tubes, 4 or 5 CO2 cartridges, boots, and a small multi-tool in addition to the stuff above.
If you look your bike and tires over
before you ride, you don't have to go crazy. I keep waiting for somebody to post a picture of their BOB trailer with the spare bike on it, just in case.
