Every year, on Bike To Work day, I stop at the Bike To Work station to get a cup of coffee, a bagel and a goody-bag. The goody-bag is a nice canvas bag containing band-aids, tube repair kits, a blinky light and informational fliers. The canvas bag, although quite nice, isn't exactly ideal for carrying stuff while riding. Fortunately, a little bit of cutting and stitching can repurpose a canvas bag into a bike-seat bag that holds:
an adjustable wrench
a spare tube
a patch kit
a spoke wrench
a tire pump
a pen
a lighter
a swiss army knife
a set of tire irons
a folder plastic bag

I should really get a small bike lock for the bag, as well as a some allen wrenches.