A few weeks ago, I made myself a bag that converts from a shoulder/tote bag to a backpack. I've used it for a variety of things including shopping, school and traveling. One of my friends saw the prototype for this bag and commented that she'd love one in a sturdier fabric to use when she rides her bike to the grocery store, as it can be easily worn either as a messenger style or backpack when her small bike basket is full. At this point, I had already nearly finished the gift I'd been planning to make her for the holidays, a padded case for her new GPS. Then I saw this challenge and decided to make the bag to wrap the GPS case.
This bag has a zippered pocket on the outside, a flat patch pocket on the inside, boxed corners and zips closed on top. It has canvas as the exterior and is lined with a layer of vinyl, then cotton. It also has fully adjustable straps, which can be used to change the bag from a shoulder bag to being a two strapped backpack.
As a shoulder bag, more like the typical grocery bag
As a backpack
And here's how I used it to wrap the GPS case.