Misc. Cheats:
Enter these on the cheat menu, then go to the code list and turn them on:

TOXICOFFENDER - All balloons are green
FREEFRUIT - Start with 10 bananas
DOUBLEVISION - Two players can use the same character
BODYARMOR - All balloons are yellow
BOMBSAWAY - All balloons are red
ROCKETFUEL - All balloons are blue
OPPOSITESATTRACT - All balloons are rainbows
NOYELLOWSTUFF - No bananas in multiplayer mode
BYEBYEBALLOONS - Computer can't use weapons
JOINTVENTURE - Two-player Adventure
TIMETOLOSE - Computer is better
BLABBERMOUTH - Changes horn sounds
BOGUSBANANAS - Bananas slow you down
VITAMINB - Unlimited bananas
ZAPTHEZIPPERS - No zippers
FREEFORALL - Fully powered-up balloons
JUKEBOX - Adds Music Test to audio menu
ARNOLD - Large players
TEENYWEENIES - Small players
OFFROAD - Four wheel drive
WHODIDTHIS - See Credits
DODGYROMMER - Display ROM Checksum
EPC - EPC lock up display
EOLAOBFENRLONE - Free Balloon

Drumstick:
Drumstick - To play as Drumstick the chicken, beat everything up through Dragon Forest. Now look on the beach part of the main world. Run over the frog with a red thing on his head.

Adventure 2:
Get the four original trophies, to unlock the secret world. In this world, get all the baloons, and the final trophy. (Giving you 52 baloons, and 5 trophies).

Take on Wizpig (the one in the fifth world, future fun land). When you win, you'll unlock the ''Adventure Two'' option. In this mode, you collect silver colored baloons, and all the courses are mirrored. In addition, you can now choose to play a course in ''Adventure'' or ''Adventure 2'' mode, in the track mode.

T.T. Challenges:
In 4 of the 5 worlds, there is a T.T. Challenge that can be unlocked by finding a key on a course in that world. Beating these Challenges will earn you pieces of the T.T. Amulet. Once unlocked, you can also play these in "Tracks" Mode.

Fire Mountain - Grab the Key on Ancient Lake. Look for a ramp on the left near the Start

Icicle Pyramid - Grab the Key in Snowball Valley. Turn directly left or right at Start to the chasm where the key is hidden

Darkwater Beach - Grab the Key on Cresent Island. At the first junction near Start, float on the water towards a pillar and go behind it for the Key.

Smokey Castle - Grab the Key on Boulder Canyon. Level up a booster to 3, ring the bell to raise the bridge and quickly boost up the raised bridge to grab the key.

Play as T.T:
To play as T.T., you must race each course in the Time Trial mode until T.T. comes out to challenge you, and he won't appear until the pre-programmed track record in a particular track is beaten by a large margin. When he challenges you, you must defeat him in a race on that course. Once you do beat him, a small T.T. symbol will appear on that particular track. You must beat him on all tracks to get him as a playable character.

Find The Fifth Secret World:
First, collect all the amulets and trophies. Next, go to the front of the lighthouse and honk at it. It will then transform into a rocket, which can take you to the space world.

Make more out of zippers:
Just before you run over a zipper let go of the A button. Instead of a small boost (the same as one blue ballon) you will get a huge boost (the same as 3 balloons).

Developer's Times:
Defeat Wizpig for the second time. After the ending and credits, a series of times will be listed. These times are the best times recorded (in Time Trial mode) by Nintendo and Rare staff during the production of the game.

Do a 180º turn on the spot:
While backing up in the car, push the control stick at an angle left or right and hit R.