I had leftover fabric from my T-shirt quilt, so I decided to make a quickie laptop bag.
This is so simple it hurts: all you need is fabric that is at least 38" long and 18" wide (or vice versa) and sewing equipment.
Fold the fabric in half so that your laptop could be placed on top of it with about .5" of room to spare on three of the edges. For me, I had to fold my fabric horizontally, as the remaining fabric was a long strip. Trim the fabric .5" from the laptop and sew two of the loose edges up, leaving the top, long part open.
Flip your bag inside out and slip your laptop in. You want enough wiggle room that you could pinch the fabric with the laptop still in, but nothing more.
With the bag still right-side-out, cut a piece of fabric to roughly the same dimensions as one side of the laptop back. With the "right" side of the fabric facing the bad (and the "wrong"/inside side of the fabric facing up), and the inside edge of the fabric against the top of the bag, pin it to the top portion of the bag and sew in place.
This is perfect for when I slip my laptop in the laptop bag I use for travel. I tend to put books and notebooks in the laptop bag as well (gotta be efficient when you're only allowed one bag on board!), so this will protect my laptop from any rough edges or metallic spirals.