the car can be used to store an incredible volume of detritus and shopping simply by making use of those oft overlooked spaces, the foot wells
Car sluttery almost deserves a thread of its own imo. 
Until recently, I worked out in the community. My car was my office, staff room and everything else. I almost always ate my lunch in my car.
The passenger footwell was the bin. It was full of sandwich, chocolate and crisp packets, drink bottles and takeaway coffee cups, post-it notes and scraps of paper with notes on that had once been important (sometimes also used as wrapping for chewed gum).
The net thingies on the back of the front seats were my desk drawers. They contained essential items like spare housing benefit and housing register forms, stapler, the welfare rights handbook, PIP/ESA descriptors, compliment slips, envelopes etc.
The back seat was my staff cloakroom. It had things like a waterproof coat (in case of sudden showers), umbrella (ditto), wellington boots (much of my patch was rural, and you never know what you might need to walk through in a rural area), a box of tissues, hand gel and anti-bac wipes (I was often required to visit homes where hygiene was way below even my low standards) and a spare pair of trousers, knickers and a spare top (put in the car after I had been comprehensively puked on by a client's child and had to drive 8 miles home, covered in vom).
The door pockets held not only the usual chargers, squeegee thingy and de-icer, but a universal meter cupboard key (clients never have them, any issue with a utility company always involves giving a meter reading), a metal tape measure (essential when supporting resettlement clients to order curtains etc) and a first aid kit (amazingly, never used in 12 years).
The state of my car used to drive DP demented. I never told him about the time an escaped apple quietly started to rot and I didn't notice until I opened the car door one morning and was engulfed by a cloud of fruit flies. Thankfully, it was on a loose mat that could just be scrubbed clean.