Racing game expansion
The racing game pack is already quite cool - but some UI/Hud stuff would make it even cooler. Trafficlights, flags. Those black and white flags for a UI background, A font that fits a racing game (maybe italic with stripes to the left). Engine sound effects would be really awesome.
Some more trees, plants and maybe water would let the maps look more interesting, too. Maybe it's possible to also support bridges?