My best haul was a 35# sack of dog food draped over the rear rack with a couple 12 packs of soda strapped to the top, and a bag of groceries on the front rack. I'm working on upping that capacity by a whole bunch by getting a Burley Nomad to do all my errands and grocery shopping.
The best I've seen was a busker here in Redmond who hauls his full drum kit (and blue tarp canopy with PVC support poles) and the rest of his belongings around on a trailer behind his bike.
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"I feel like my world was classier before I found cyclocross."
- Mandi M.