It is made from 54, 3 round dc granny squares (9 of each color) with a single round of sc in black for edging.
I used a real cube to design a pattern to join the squares and made the 6 sides each of nine squares using black to join them. I also blocked them. It the peices moved it would be possible to make solve it.
I then joined the 6 sides to make a cube leaving I side with 3 open edges.
I also made a shoulder strap in black using dc and sc rows of the colors used in the sides. I made it twice as wide as i wanted it so that i could made a tube and insert seat belt webbing to stop it from stretching to much when used.
I then made a black fabric lining with a pocket and sewed in the lining and a zip with the handle in between the lining and outside.