Confession: I cheated.
I was going to make Imogen a fancy backpack from an Oliver+S book, but I decided the pattern was a little too difficult for my current skills. I have the pieces cut will be made...eventually. And without a time pressure (I "needed" to finish it for her first day back to preschool).

Lucky for me, Purl Soho sent out an email with this pattern. Done.

I'm guessing Immie is just as happy with this "packback"as she would have been with the other one.