To resurrect this old thread with a solution that has been working great for me. I bought a storage container from Menard's that is 17"x12"x8", which fits perfectly in the floor in front of the back seat or passenger seat. It is a stainless steel decorative type thing, but there was nothing else that had this exact dimension. All of the Tupperware type plastic ones were either too big or too small to be of any use.
Then, I looked around for something that could be used as a "chute" to attach to the container and bring within reach if the driver's position. I found a plastic gutter extender that is easy to cut, made a bracket that lets the lower end hang onto the lip of the storage container. The other end of the chute is secured with cable ties. The container can then be pulled and dumped when it gets full, and everything from small wrappers to big coffee cups and bottles is contained and out of sight.
I haven't found any trash bag liners that would fit well here, but keeping my eye out.