The 8-year-old didn't appear to be distressed when fire service arrived around 7.30pm.
"By the time we got there he was drinking a can of drink."
The boy's grandmother was "just happy he was out."
Clement has been in the fire brigade for over 30 years, and this isn't the first time he's been called out to attend to kids stuck in unusual places.
"I've seen kids stucks in trees and kids with legs stuck in bench seats."
New World Foxton has apologised to the boy's family for the distress caused.
The donation box's slot measured about 15cm by 30cm. It needed to be wide enough to deposit bigger groceries but not so wide that they could be stolen.
While no such incident has occurred before, Foodstuffs is working with the box's owners to find a solution to ensure it is not repeated.