What you'll need:
1. Fabric, I use a yard and that makes more than enough for two bags with lots of piping plus you will have yardage left over. A half a yard would probably be more than you need for one bag.
2. Cording, I use 6/32 cording from Joanns. You can find it in the home decorating section. For a bag like the Weekender by Amy Butler you need 5 yards (I make 6 yards just to be sure I have enough). For a bag like the Vivian by Swoon you only need 2.5 yards.
3. Steam a Seam, you can purchase this at Joanns as well in the notions section. It makes things really easy.
Fold the selvage edge on your left side down to meet the bottom edge, forming a triangle.