If you have a manual transmission, a bespoke shift knob (you can check out one that I did here: Shift Knob V2 - Walnut Goodness)
I really like how solid walnut comes out, when solid wood is appropriate. Laminated high quality plywood (like baltic birch) can also give you a really slick look. I haven’t tried any faced plywoods, but I’m sure they would look good for flat parts.
If you’re into custom audio in your vehicle, any speaker or electronics mounting enclosure could really benefit from a good looking wood surround or enclosure.
Another fun wood is white oak - which can be a great accent against walnut. Have fun, and make sure you show us what you do end up making!