It seems as though the day pack has become a sort of fashion statement for urban street riders...
Urban riders use them because we also walk a lot and need to carry our stuff with us. In the DC area, even the cage/train commuters wear backpacks. Many of us have work-issued laptops, lunch coolers, etc. in them. People also run errands on the bikes, too. A backpack is any easy way to store everything one needs for a ride and just have the one item (the bag itself) to grab instead of a checklist. Urban mobility/commuting is a totally different world than rural/leisure riding, that's for sure. It's also why a lot of us have small displacement motorcycles and mid displacement scooters even though we've been riding for years.Yeah, I hadn't really thought of the fact that a small backpack would be convenient for running errands going to stores and such.