I found this design Here . Like the sandwich wrap it is very easy and quick to make.
I cut out two rectangles 14 inches x 7 1/2 inches out of cotton print fabric. Cut out paper backed iron on adhesive into a 7 1/2 in x 13 in rectangle. This is the type you would use for applique. The first bag I made I cut it out the same size as the fabric. After making it I decided it would turn better if you did not have the cereal bag above the Velcro. The second one I made I cut the adhesive in a 13 in x 7 1/2 in rectangle. Leaving about 1/2 in on each end. You will adhere this on the right side of your liner fabric.
Next, pull off the paper back and adhere the cereal bag to the fabric. I did this by placing the cereal bag onto the fabric. I used the paper from the adhesive as a protector. Lay it on top of the cereal bag and iron.
Now fold each rectangle in half lengthwise. Cut out a 1/2 square off of the bottom corners along the fold.
Cut a strip of Velcro 7 inches long. Sew each side of Velcro about 1/2 inch from the top. The first bag I made I did it about 1 inch down. I prefer it a little closer without the cereal bag at the top. Sew the Velcro on leaving a 1/4 of fabric on each side.
Now sew your seams. Fold bag in half right sides together and sew the seams on each side using a 1/4 inch seam allowance.
Now you make your box bottom by bringing the seam to the corner. Trim to make it even and sew a seam leaving a 1/4 inch seam allowance. I go back and forth on this seam several times to ensure it stays put!
Turn the outside fabric right side out. Put it inside the liner fabric. Line up the seams and sew around the top using a 1/4 inch seam allowance. Leave a section 2-3 inches long open so you can turn the bag.
Turn the bag right side out. Then top stitch around the edge stitching close to the edge. Your snack bag is now done!! It truly is water proof. My kids used it once and I rinsed it out. I filled it up with water and sat it in the sink. The outside never got wet. You could drink out of it!! You really can't store liquid in it because it would seep out of the Velcro, but it will keep wet things in there without getting other things wet and sticky.
After making the first bag my kids started fighting over it. So I had to quickly make another one. As you can see the bags are slightly different. The first one I cut a 15 in x 7 in rectangle. The second one I cut a 14 in x 7 1/2 in rectangle. I prefer that size better. The black bag is the second one which I gave the directions and dimensions for.