Bike Messenger Bags – Best Price!

Messenger bag for general usage, vs. backpack, fanny pack, seat bag, trunk bag–what are the +/- of each? For messengers the m-bag looks best for carrying flat packages, quick access, and flexibility, but what about for general, random usage on a bike? Carrying books, or shopping, plus a jacket, a snack, bike tools, spare tube, commuting, etc? What’s best for general purpose in your opinion? What are the best usages for messenger bags? Thanks BSG!

thanks for the review!