When Mandy starts the parade, the camera ends up on Joe sitting in his car, the words "Flatch Rocks!!" can be seen on the window behind him. When the camera cuts to inside the car and Joe pouts with "This sucks", the words "Yay! Party!!" are seen on that window instead, as well as later shots from the same camera.
When Kelly is driving the truck in the parade, all interior views clearly show its speedometer and tachometer both reading zero. While the key is in the ignition, it remains in the "off" position. This would indicate it's being towed on a low-profile trailer with the engine off.