In the leap from the pseudo 3D in Super Mario Kart into true 3D, Mario Kart 64 introduced some new items. These includes the Super Mushroom (AKA the Golden Mushroom), the Fake Item Box, the Spiny Shell (AKA Blue Shell), and various triple variants of previous items such as, the Triple Mushrooms, the Triple Bananas, the Triple Green Shells and the Triple Red Shells.
Correction
Um actually … Mario Kart 64 does not have Triple Bananas. It has Banana Bunch instead, which gives a trail of 5 bananas. Triple Bananas is introduced in Mario Kart Arcade GP instead.
Just replaying the sound of releasing bananas from memory is enough to know it was 5.