Definitely the Deuter pack. 20-30L should do for your stuff. They make cycling-specific packs with reflectorized loops to hold a blinkie, hydration packs. I use a 25L pack and it holds all my commute stuff with room to spare. I tried the TransAlp 25L pack recently and loved it. Lots of pockets and even a removable backpad (they claim for sitting on but it wasn't so easy to remove). Love their built-in raincovers too. I don't use the hydration bladder so that is one more pocket for me to stash stuff in.