Neat in both the colloquial and literal meanings of that word.
Not my pattern. You can find that HERE. (I ran out of the dark blue cotton so used the turquoise to finish up.) It weighs about 70g including flower and button so could be made with a 100g ball.
Here is the bag laid out. What is the little touch of yellow? You will see in a moment!
The base is two thicknesses and creates a pocket for the bag.
Here it is emerging from the pocket. Tuck it all in and you get – (I rescued the button from a birthday card!)
And a view from above. Just right to pop in your pocket in case you need a bag!