In Homer's last level there is an RC car hidden somewhere in the city. To find it go to the Krusty Burger with the firetrucks next to it. Go to the second firetruck and jump on the ladder and head for the firetruck's roof. There will be a mini RC car and a Bumblebee camera. Destroy it and have fun with your mini RC car.

Level 1 Rocket car: Outside Quimby's mansion
Level 2 Monorail: On monorail track near Itchy and Scratchy balloons
Level 3 Night boat: On the boat where you find Bart (stashed in a crate)
Level 4 Quad bike: In the caravan park near a tree
Level 5 Monster truck: Near the stadium above the fountain
Level 6 Pink Caddylic: Hole in a wall next to Planet Hype
Level 7 RC car: On top of Krusty Burger near the Kwik-E-Mart