Lets see, I use a JanSport "Big Student" backpack with 5 pockets. It gets hooked over the back of the seat of my Bacchetta Giro 20 or worn when I ride my Specialized Hard Rock. It has a modified reflectorized safety vest as a cover.

1st Pocket - 4 AA batteries, 3 pens, a tube of lip balm, two reflective pant straps and a pair of ear buds.
2nd Pocket - Sunblock, Sunglasses and another pen
3rd Pocket - Cell Phone, Charger and a data stick
4th Pocket - Kryptonite U Lock
5th Pocket - 2 local weekly papers, folder with paper pad in it, 1 plastic grocery bag with spare tires(20" and 700cc for the recumbent and a 26" for the Hard Rock), 1 plastic grocery bag with pump, patch kit, tire levers, 1 plastic grocery bag with another pen, calculator, 8 bus schedules and a baggie and rubber band to put over my headlamp if I need to ride in the rain, 1 plastic shopping bag with spare dress shirt and underwear for work, and a curly cable lock.
Mesh Pocket - one water bottle from the Community Bicyclist.

In addition to this I may need a raincoat, or multiple layers of clothes.

I keep my rear blinkie on my helmet.

Both my commuting bikes are equipped with street slicks, racks, fenders, lights, reflectors. Neither has a bike computer.

The only thing I would change would be the saddle on the Hard Rock. Seems like they have fitting a bike down to an art, but fitting a saddle is a complete mystery that they say just keep trying them till you find one that fits. That doesn't make sense. I think that people havent worked hard enough on that problem.