This modern messenger bag is knit on large needles with double-stranded wool, and then felted. The entire bag is knit in stockinette stitch, mostly in the round, and is seamless. Small gussets give dimension and the I-cord detailing adds a finished look. I rated the difficulty as tangy, but really anyone can knit it. All your mistakes will be felted away.  

Small Size: Sized to fit a manuscript book & papers, or a small notebook computer

Large Size: Fits a larger laptop computer; sized for use as school bag or carry-on luggage

-- Description from Knitty.com