Finding good roommates is hard, because most people have domestic idiosyncrasies that a) they're unaware of and b) they can't shake. I've had roommates that turned the kitchen garbage can into a game of Jenga, stacking and balancing one piece of trash onto another rather than taking it out. Me on the other hand, I'm a garbage compressor, a habit I picked up in Japan.
When I was working in a school there, after lunch I observed each student cleaning up after themselves as taught to do. Each and every one took their regulation milk carton and folded it completely flat before placing it in a clear recycling bag in the classroom. When all the bags schoolwide were gathered up for collection, it became obvious why they flattened the cartons: The entire school's worth of discarded milk cartons fit in just a few tidy bags. Less plastic bags were used, saving some plastic there, and this also made more room in the recycling truck. District-wide this resulted in less trips made by the truck, less gas used, and less exhaust fumes. These savings were achieved by hundreds and then thousands of students performing a ritualistic two-second act after their meals.
I was reminded of this when I saw the Smash Can, a kitchen garbage can that has a sort of accordion built into the lid. Press it down and it compresses your trash without getting your hands into contact with the refuse. Not as efficient as hundreds of thousands of students folding something completely flat, but a good start.