The pattern was from the Design Collective's Lunch Bags book that I have used before.
The process was relatively straightforward. The bag consists of one long piece, and two side inserts. The insulated wadding is attached to the outer fabric.
The shoulder strap/handle is added to the outside. I added a tab on the side away from the bottle to avoid the side gaping.
I hope the bag proved useful to my sister-in-law for taking her lunch to work each day - or for picnics or snacks at the beach.