This is a fun little project for the beginner and it will save you lots of money. Cup Holders start at about $19. This little project cost about $4 for two Cup Holders. I bought the Cup Holders and Carabineers at Walgreens. The Carabineers are the type made for keys. They are not heavy duty but they only have to hold a can of soda in a cool sleeve. I didn't count the brass screws and nuts because I have a screw caddy full of left-over and new screws and fasteners for quick little projects like this.
An improvement would be to figure out a way to have the Carabineer centered above the center of the Cup Holder. I might try replacing the piece of wood with a piece of flattened copper tubing bent to center the carabineer. So for now you'll have to take a couple of swigs of your soda before putting it in the holder as it tends to lean forward a little.