Devon (of Tron submission) sent along the following hack for making a waterproof messenger bag out of an old dog food bag. In his email he made sure to tell me that Crystiana gets credit for the hack, and he gets credit for being the photog. Take it away Devon and Crystiana!
Gather your materials. You will need: cat/dog food bag (plastic), velcro, straps (you can scavenge these off old duffel bags from the thrift store), and fabric for exterior.
Figure our your dimensions. Be sure to leave a seam allowance. 1/2" seam allowance is a lot but its good if your just getting used to sewing/using a machine. We modified the templates given here -
You can make a mock-up out of news paper to decide how you like your design.
Cut out your pattern from the cat/dog food bag. This will be the interior of your bag.
Crease. This will make it easier to sew your seams together.
Ta-da! Half done bag.
Sew on your straps.
Cut the exterior from your fabric. Same pattern as cut from the dog/cat food bag.
After sewing the fabric fit the bags into each other.
Put on the velcro or straps to hold the flap down.
Add any embellishments.