Once I found a great blog entry where somebody showed how she’s working her stash and scrap yarns into a scarf. Unfortunately I don’t find the entry back ;-(
In principle she sorted her stash according to colours (her example was made in blues) and from each yarn she crocheted a long row, every row even in another crochet stitch.
I hope that the photos are a help.
I found the result so stunning that I made a birthday gift for a good friend from it ;-)
By the way, this can surely be done in knitting, too!?