If they're really junk and short pieces, I color coordinate as much as I can, use large needles and multiple strands, then knit them into floor mats, mats for under potted plants, dog beds, cat mats -- you get the idea -- anything that goes fast, has a purpose, and doesn't need to be pretty.
If your scraps are nice and go together well, you could make towel rings, potpourri bags, curtain tiebacks, tassels, pompoms, or coasters.
If you have a whole lot altogether, you could make a "hobo afghan." Just start knitting. When you run out of one color, add another. Leave the ends long and leave them hang when you add a new color. The result is a super casual, sloppy, fun item that always brings a smile. If you don't have enough for an afghan, make a throw, lap rug, or foot warmer.