I like to keep my car clean, and I've found the best spot for me to put a stray wrapper or empty can or cup while I'm piloting the scow is in a bag behind the passenger's seat. I used to have a reuseable bag in my VW Beetle that I'd throw stuff in, but to empty it, you'd have to take the seat cushion up and off... which in a Beetle means sliding the seat all the way back, then tipping it all the way forward... with a full bag of trash.
These hooks snap onto the 17mm diameter uprights of my seat cushion in my Ford and drape over the back of the seat to hold a standard plastic bag, or a small reuseable. It's not the most amazing aesthetic solution ever, but it does keep it classy in my ride.
This is palleted for an Up! Mini... just orient the little 2mm spacer norker down towards the build platform and hit 'place'. Derafting is not difficult.
Just hook over the cushion upright and give it a little tug and it should snap on. It's sized for 17mm, so anything smaller should work OK. If you're fussy you could scale it to fit, since none of the other features are critical.
These parts didn't need to be mirror image; they both could have been the same part... but it looks nicer this way.