You've run wild in IKEA (again) and had to buy one of those big blue bags to get everything home. Rather than leaving it to languish in the garage, convert it into a nifty messenger bag.
At IKEA Hacker, Sara details how she converted the bag (known as the Frakta if you're being formal) into a messenger-style satchel using a few spare parts and "lots of swearing from getting pins in my fingers". This isn't the simplest hack in the world, but the end result is pretty neat. For a different IKEA bag approach, check out the placemat netbook bag.
Ikea blue shopping bag into messenger bag [IKEA Hacker]