To see the Dopefish, a creature from Commander Keen, start any single player
race.  When everybody else moves, stand still.  Hold down the break, and turn
left all the way around until the Dopefish shows up.  Note:  the lion that
starts the race must remain on the screen the entire time; otherwise, the
Dopefish won't appear.  You can do this as many times as you like, so long
as the lion doesn't leave the screen.

Also, in the shareware version of the game, there are two ways to play the
track shown in the ordering information of the shareware game, which is
supposed to be a track available only in the registered version.  One way
is to play in Championship Mode; you will play that track as a bonus.  The
sneakier way is to exploit a loophole.  Start a new game, and complete
track 1.  Save the game, and quit to the main menu.  Now look at the ordering
information.  Go back to the main menu, restore the saved game, and voila.

There's an inside joke in the game that appears when you select your engine
power (6 or 12 horsepower).  The caption on the screen reads "Lee & Jackson
Lawnmowers."  The story behind this is that Lee Jackson (at that time not yet
promoted to Music and Sound Director) made a comment at a beta conference that
the go-kart engines sounded too much like little Briggs & Stratton lawnmower
engines.  The game's programmer, Andrew Edwardson, got Lee Jackson back for
this remark by including the caption -- "Lee & Jackson," split up in the same
way "Briggs & Stratton" reads.