Practice track traffic:
Complete a regular game and return to the title screen. Press C to enter the options screen and enable practice mode. Hold B + C, then press Start to begin game play. Traffic will now appear in practice mode.

Race against the Phantom on the Speed track:
Turn right instead of continuing forward on the championship lap. Go over the turn signs and race against the Phantom on the speed track.

Cow trick:
Hit the cow standing next to the barn at the start of the stunt track to hear it "moo".