The Nintendo 64 Controller Pak was used in certain games to save data that could not be stored on the game cartridge itself. It was used to save ghost data in Mario Kart 64, and to save the game itself in Quest 64. Most games published by Nintendo saved their data to the cartridge itself, and many third party games required the Controller Pak to save data.
Trivia
The Canadian variant contained English and French languages on the blister packaging. The Controller Pak itself is the same as the North American release.