As the BMW i3 has some pretty unique seats, the great "Car Headrest Bag Hooks by muzz64" (inspiration-link) doesn't fit.
Luckily I could remix the "Parametric hook with backing plate by ZombieFeynman" (https://www.thingiverse.com/thing:3722448), add the "BMW logo by YusufGP" (https://www.thingiverse.com/thing:4576411) and use an old shoe lace to tie the hooks to the headrest, to keep my stereotypical tote bag from falling over (once the EV is driven less stereotypical).
ZombieFeynman used GPL, so this remix also does.
If you want the BMW logo on it (like depicted), download the STL seperately and compile it with the according parameter set to "1". (Corporations sometimes get funny ideas about usage of their logo, so I don't share it here...)