In five years of Model X ownership, the only accessory I bought was a little metal frame thingy for the key so I'd be less likely to close the boot on my head
I'm tempted to get some of those S3XY buttons and maybe a mini display for the Model Y, although that's mostly to get around what I consider to be deficiencies in the user experience. I've never really thought that much about all the things you folks are looking at! Are there any that you consider must-haves?