Napkins, tote bags, and pillowcases have all been mentioned. And there is nothing better for sewing knits than a serger! I loved making tshirts and sweatshirts for my kids with my serger. I made fleece socks one year using a flat lock stitch. Those were a hit!
As for using it in quilting, I have recently started serging the edge of my quilts prior to binding them. Gives me a nice solid edge. The serger is really for home dec and garments though.