Made a couple of updates to the backpack after my son (8th grader) had put some miles on it. 
First, I made new shoulder straps, the single thickness straps weren't beefy enough for as much stuff as he carried around.  I sewed two pieces together to make it double thick and made them 2" wide where they ride on the shoulders.  Then I stitched two 1" wide pieces together for the bottom portion of the strap. 
Second, I added some grommets and drawstrings to pull the top closed. 
Third, if I were to make another, I'd double the thickness of the handle as well.  He uses the handle a lot to quickly pick up / move the bag, and the single thickness handle is showing some significant wear.  It's still holding up, but a double thick handle would be a lot better.