We might make a lot of junk, but our trash can is all kinds of smart.
Project cost: Less than $9
We used to just hang a plastic grocery bag from one of the hooks behind the front seats when we needed a trash can. It didn't work very well as the mouth of the bag wasn't held open, it was in the face of anyone who sat in the passenger seat when it had been spun around, and it was too difficult to reach when hung up behind the driver's seat. (You can see what hook I mean in this pic, it's the white thing attached to the B pillar.)
While on our Honeymoon, we decided we needed a better option and found one in some random Utah Walmart. It's a Promart Industries Popup Laundry Hamper and it retails for less than $9.
When not in use, it stores nicely in a flat little package just about anywhere.
Because we stopped at Lake Mead (if you're thinking about it, don't) during windy season, the bag we put inside the hamper just kept blowing around - inside the hamper, outside the hamper, everywhere. So I held it in place with clothespins (handy little buggers, we always have a few floating around the van.)
We recycle (does anyone not anymore?) and so we now put two plastic grocery bags inside the hamper - one for trash, one for recycling - and hold them in place using a total of six clothespins. The clothespins (to make sure they're available when I need them) are stored inside the folded up hamper. Easy peasy.
We then set the hamper on the driver's seat (it can't turn around very well anyway given our new console) and it's super easy to use and not in the way at all. Sometimes we put it in the driver's footwell if we need the seat for something else.