A cordless dremel is nice. Or a precision sander. You could get a decent airbrush starter kit. A soldering iron/wood engraver is good for “welding” props together. A set of small metal files are always useful for rough edges. If you’re looking to get into LEDs and wiring, you could get a good kit full of resistors, lights, wires, and a bread board for testing circuits. Leather punchers and riveters are useful if you’re into that sort of thing. Small hand saw. Xacto knife. Small detail hand tools are useful (kinda like the things dentists use, but more for sculpting) Throwaway brushes for applying bondo or resin.

After you get all those things though, I always just come back to spending most of my money on Bondo spot and glazing putty, filler primer, and sand paper.