I bought a large beach towel for Basil some time ago. It stays in the trunk of the car, not to keep the trunk clean, but so that I can flip it over Basil and keep him out of sight, particularly on road trips.
On general principle, I think it’s best to keep valuables under wraps. And what, after all, is more valuable than my Brompton? Basil’s bright towel ensures that I can open my trunk without advertising that he’s traveling within.
But, really, how often do I open my trunk while traveling? Typically I open it only once at night, when taking out Basil (and luggage, the first night), and then each morning, when I put Basil back into the trunk and we head out for the day, and then once again at night when Basil returns to my room with me. It’s not as if I spend my days shopping, and am popping open the trunk every hour or so to store stuff in it.
(What? Of course Basil stays in the room with me!)
This is probably one piece of “gear” that wasn’t strictly necessary. On the other hand, if I cared about my trunk getting messy, all that washable fabric would probably be an asset.