Molly Weasley's self-knitting blanket is possibly my favorite knitted item in all of the Harry Potter movies. I've wished more than once to be able to charm my own needles into whipping up projects while I sleep, I assure you! And while I've yet to master this skill, making a blanket like this might just make up for it.
While no pattern exists (yet) for Molly's Blanket, the pattern looks easy enough to replicate with slipped stitches. Simply cast on your desired number of stitches and work in stockinette, slipping every other stitch on the row WHILE you're changing colors. That will carry the previous color up to the next row without having to do any stranded color work. What a great way to use up leftover bits!