Breakfast, lunch, wallet, work ID, a plastic bag, two spare tubes, a pump and the rain cover for the bag.
I used to carry tools but in 12 years I never used any of them, I'm never more than about 6 miles from either work or home where there are tools, so in a rare case where I might need them, I'll just walk, walking is good too.
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Work: the 8 hours that separates bike rides.