Custom painted Jack O' Lantern hubcaps?
Even plain orange would look cool with black tires.
A black, orange and purple Halloween wreath wired to the front grill.
If it's a stick-shift, a pumpkin or skull knob for the stick.
A high quality figure of a broom-riding witch to hang from the rear-view mirror, something nice.
Halloween-themed floormats.
See if you can find a really cool hood ornament, like a bat, a skull, something.
If it has an antennae, get a Halloween-themed ornament for that.
Bloody hand prints on the rear window, to the side so as not to block vision.
Fluorescent triangle eyes and a toothy grin on the back, for those travelers behind you on dark nights.
Even plain orange would look cool with black tires.
A black, orange and purple Halloween wreath wired to the front grill.
If it's a stick-shift, a pumpkin or skull knob for the stick.
A high quality figure of a broom-riding witch to hang from the rear-view mirror, something nice.
Halloween-themed floormats.
See if you can find a really cool hood ornament, like a bat, a skull, something.
If it has an antennae, get a Halloween-themed ornament for that.
Bloody hand prints on the rear window, to the side so as not to block vision.
Fluorescent triangle eyes and a toothy grin on the back, for those travelers behind you on dark nights.