I initially started quilting free-motion squiggles all over the quilt, but after doing about 1/4 of the quilt, I decided that style didn't suit the quilt and I spent four hours ripping out the stitches. I decided to do straight lines of quilting around each of the flags, and then more lines inside the triangles. I left the quilting lines as far apart as possible so that the quilt is still soft.
I backed the quilt with a twin flat sheet from Target (100% cotton and less than $11!). The quilting was all done with light grey thread, so it blends into the grey backing fairly well. I like that you can still see the quilting lines, though - it gives the back some interest.
I bound the quilt in this awesome sketchy crosshatch print from Jo-Ann's. The print is black and white, which captures the color scheme of the quilt without matching too closely to any of the flags.