Collecting all four letters (K, O, N and G) earns the Kongs an extra life. K-O-N-G Letters are entirely optional, as they do not affect the game's % complete. The letters also serve as a way to show the player how far he or she has gotten in a stage, as they roughly occur at each quarter of the stage. There is generally only one set of K-O-N-G letters per stage.
Donkey Kong Country/Land series
These items appear in the Donkey Kong Country and Donkey Kong Land series as collectible items in every single stage.
A few stages in Donkey Kong Country 2: Diddy's Kong Quest have multiple KONG letters to allow players to get the full set when using shortcuts or alternate routes. K-O-N-G letters also appear in some Bonus Stages in the original Donkey Kong Country. These mini-games required the player to jump and collect the letters in a certain order, to spell either 'KONG', 'NINTENDO' or 'RARE'. An entire alphabet of letters appears the game's coding, although most of them are not used in the game. 
In Donkey Kong Land, the K-O-N-G letters do not grant extra lives and are instead used to save the game. If the player finishes a stage with a full set of K-O-N-G letters the game will be saved. In one stage in this game, this has an even stranger use for K-O-N-G letters. The player collects the four letters in rapid succession before jumping on an industrial fan. This blows the letters across the stage where they can be used as platforms. This is repeated for three sets of K-O-N-G letters; only the fourth and final set can be used for saving the game.
These items reappeared in Donkey Kong Country Returns as once again, collectibles in each stage and, this time, affect the player's score in the game and are orange with yellow text. Collecting all the kong letters in a world will unlock a difficult secret stage. Completing all of the secret stages will unlock world 9-1.
Diddy Kong Pilot
These items were to appear in Diddy Kong Pilot as collectibles in each course.
DK: Jungle Climber
These items reappear in DK: Jungle Climber and act the same as these items did in the Donkey Kong Country and Donkey Kong Land series.
|Items (not barrels)|
|General||Animal Crate • Animal Token • Banana (Bunch) • Crate • End of Stage Target • Extra Life Balloon • Golden Feather • Kannon • Kannonball • K-O-N-G Letters • Mine Cart • No Animal Sign • Skull Cart • Tire • Toboggan • Treasure Chest|
|Coins||Banana Coin • Bear Coin • Bonus Barrel • DK Coin • Kremkoin • Kong Token • Nintendo Coin • Rareware Coin|
|Others||Banana Medal • Cog • Crest|
|Micellaneous||Brothers Bear items|