The Kakadu Bag was chosen out of its uniqueness and complexity in organic props. I started modeling before Zbrush really hit the market so I had started modeling the "old school" way of pulling polys. It was good prop to really push my traditional organic modeling skills in max and to show that not everything has to be done in Zbrush nowadays.
I started by blocking out the main form of the backpack around a box. The box was to represent books that would be in the bag so that, while modeling, I can model the mass and form of the bag interacting with what would be inside.
  Using cuts, insets, and target welds, I begin to shape the bag around the box on the inside keeping in mind the dynamics of how canvas actually folds and reacts. Soft selection is a huge help through shaping the bag. Through this entire process I am trying to not care too much about poly flow and whether or not I am using triangles because it is just going to be cast down to the lowpoly in the end.
A good portion of the folds and wrinkles are now done and I start adding details like seams in the bag and the extra strips of cloth on the back. The lip around the flaps were created by extracting a spline and running the sweep modifier on it.
  A leather strap was made, copied around, and bent to fit each area. Buttons and stitching were added as I was reaching the final detailing stage in the model.
To see how I approach highpoly stitching, check out the video in my tutorials section HERE.
  I was trying to figure out a fast way to get the lowpoly started for this piece, so I ran most of the bag through the decimation master in Zbrush. A few of the pieces I was able to salvage out of the highpoly by collapsing in the meshsmooth and ripping some edgeloops out.
  To start reducing the lowpoly, I began collapsing and cleaning up all the unnecessary geometry. Through this process I kept the highpoly underneath so I could keep a close eye on the silhouette of the lowpoly in comparison to the highpoly. In the end a lot of details were merged together and cast as one to save on tri count.
  The unwrap was pretty challenging because there were so many varying shapes. I tried to put seams where there were natural seams on the bag, and where least visible. I allowed a bit of distortion in some places, due to some edges that I forced straight for better packing, but in the end it didn't pose a problem.

The straps and a few leather straps were all mirrored so that UV space would be saved for the body of the bag.