Work ID/security card, a thumb drive, sunglasses, spare tube, tire levers, cheap multitool, phone, camera, credit card, PB&J sandwich for breakfast, container of leftovers for lunch. Every 2 weeks or so I'll bring a pair of jeans and 4 or 5 shirts to trade out what I've been wearing for a while. A new towel about as often.
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Work: the 8 hours that separates bike rides.