I didn't use a pattern and winged it a bit, however it is just an oblong piece of fabric cut with a point at one end, and folded up to make the bag and pointed end folded down to make the flap.
The piece of gingham sewn on the front forms a pocket and the flap is also lined with the gingham. I finished off with a button hole, self covered button and matching strap.
This is the lucky dog whose treats will be contained in the bag, he was about 6 weeks old in this picture. He is now at least 4 times as big and still growing.
I hope my sister in law likes it, I have wrapped it up and sent it to her to open on her 50th Birthday.