I saw this idea somewhere online and I thought it was genius. I also saw a version on here, but I didn't base mine off of it--is used a plastic bag to line and put fabric on the outside to make it sturdier. Good idea, I am just trying to eliminate as much plastic as possible from my world (haha, yes, I know there's plastic in velcro).
Basically I just cut two rectangles, hemmed and sewed on the velcro on the blue part, then sewed up the sides to make a pouch. Then I made the outside almost the exact same way minus the velcro. I put the blue pouch in the black and white pouch, stitched along the bottom to keep the liner in place and then stitched around the mouth of the bag to join the two pieces. It worked out well, but sewing the top proved a touch tricky for me (I am all self-taught, so some things are still a little tricky for me if I haven't tried it before). I might make a tutorial when I make another bag (it works well so far!)
Oooo! I found the website...I posted it there. I wish I'd had it for the making of this! Haha!