Think that pack fits a laptop, mouse, a few small accessories, and a pair of large jeans, shirt, socks, underwear and still use the reservoir?

I've used my daughter's Columbia Treadlite 22 liter. It's back draft suspsension system is very well designed, and the pack is very light. It's a little small if I want to carry a lap top along with the other things I would normally pack. It's not specifically designed for bike commuters, but perhaps for the money it's a better value than the Ospreys or Deuters.

I use the Camelback Mountain 14er. Vented back and plenty of space for clothes and food. I carry water on the bike but use the water bladder when I use the pack for hiking. $100 and couldn't be happier with it.

I realize the OP found something for him, but wouldn't it have been possible to just get a single sling messenger bag? Or a handlebar bag?