Cut your fabric. For the bag pieces you want your fabric to be 15×32 inches (so one out of both the outside fabric and the inside fabric. For the strap piece you want it 5x 42 (or whatever the width of the fabric is). You can do the strap shorter or longer depending on your preference and fabric.

Fold the bag pieces in half length-wise so that the right sides are together and sew down both side edges.

Then turn the outside fabric right side out.

Tuck the lining fabric into the outside fabric.

Fold the edge of both pieces under 1 inch and iron.

Fold the strap in half lengthwise with right sides together and sew down the long edge. Turn right side out and iron.

Tuck the ends of the strap between the folded edges of the bag pieces at the side seams and pin.

Sew around the top (folded edge) of the bag catching the straps. Do a second row of stitches to reinforce the hold on the strap. And you’re good to go!