A can holder that clips on the top of your 2013-2014 XF/M (likely more years and models compatible) gas cap.
The holder accommodates a 355 ml can with neoprene koozie.
3D model found here if you want to tinker - https://cad.onshape.com/documents/10800bcf94f53c02fd5a3e71/w/b4bd14e175593fb95cd42e2c/e/85873adce12106c3e8ba40b4?renderMode=0&uiState=6524b18e78e5e64d0369409f
The author marked this model as their own original creation.