A messenger bag is not the most practical for carrying a laptop, notebooks, etc...that you listed. A backpack is the most practical, easy to find, and least expensive. A decent messenger bag is around $100 or more. A backpack of similar quality is around $50.

Messenger bags are/were used by bike messengers because:
A) They had to carry unusually sized packages at times
B) They are in and out of the bag frequently. This is why they just slide it around the shoulder instead of taking it off.

Commuting to work or school you likely have the same load daily and you only go into the bag when before you start your ride and when you reach your destination.

Messenger bags are generally cavernous and your stuff gets majorly mixed up inside.

I have a *thing* for bags. I currently have (not counting what I've sold or given away) 5 backpacks and 3 messenger bags (Chrome, Custom Timbuk2, Nike). I almost never use the messenger bags. I sometimes use my huge Chrome bag as a weekend bag when I fly. The other 2 I've probably never used. Seriously.