Fifty lives
On the start page select "Exit game". On your controller: push 
, 
, 
, , , 
and hear a ding! Play the game and you will see you have fifty lives. Do it wrong and it erases a saved game, so be careful!
Also on the SNES this is possible with the same buttons(just a different controller). On the SNES version of the game, doing this cheat wrong will not erase a saved game.
Bonus Game Trainer
While Cranky Kong is doing his music and stuff, hit 
, 
, , , and you will hear a ding. You will then appear in a bonus room with 3 of each Animal Token. Here you can train your skills at the bonus rooms for the animals (Rambi, Expresso, Enguarde, and Winky).
Kill a Klump with Diddy Kong by jumping
If you are playing as Diddy kill any extra enemies around a Klump. If you can jump on him long enough to get him to fall off an edge, right before he falls he will die.
A Darby Day of Music (Music Test)
Highlight erase and insert the following code.
, 
, 
, 
, , , , . If you hear a ding, push 
to change the music.
Donkey Rides A Donkey
In Jungle Hijinxs, get Rambi from his box and go back to the beginning of the level. Go up the tree and jump on the next tree. Jump where the banana arrows are and get the Metal Barrel. Throw it at the tree house tree and jump on it. While riding it, hold and when you get to Rambi (while still riding the barrel), push . Suddenly you will get on Rambi, Rambi will become a black and red Donkey Kong, and the B&R Donkey will throw the barrel (but he actually throws the air, because the barrel mysteriously disappears). You will then ride an almost fully-active black and red Donkey Kong. But if you hit anything other than 
and 
, the DK will disappear, and Rambi will return. This same thing will work if you use Diddy to ride, only it will be a black and red Diddy.