Cameron Baldwin tried to get his mum, Nici, to buy $20 of bananas in the hopes he could get one more Dreamworks Heroes card.
The Rotorua 9-year-old is among thousands of children up and down the country trying to complete a set of cards based on movies.
Rotorua's Countdown staff are bracing themselves for an influx of children tomorrow as they host in-store swap meets.
The stores have been part of a nationwide promotion where cards are issued for every $20 spent and when certain products are bought.
The collections feature characters from Dreamworks movies, such as Shrek and Madagascar.
"When I'm older I'll get a lot of money for them," Cameron said.
"They're fun and I like the movies - The Croods is my favourite. I was excited when I filled my first book, I was the first in my class to complete it."
Cameron has been collecting since the promotion started this month when he and his parents were on their honeymoon in Christchurch.
He's since started a second set and that is almost complete.
To help him collect the 42 cards required for each book he has enlisted the help of his mum's two sisters, one of whom lives in Wellington, and they have changed the supermarket they shop at.
Mrs Baldwin said she shopped online and would usually top up milk and bread at New World but has been going to Countdown instead.
"I think it's crazy how something so simple has gone so viral," Mrs Baldwin said. "He's been making me post on Facebook to get swaps for them and on the work intranet. We had to go to Starbucks on Sunday to swap cards and then on the way home he wanted me to buy $20 of bananas to get one more card."
The promotion has been such a hit that the albums that store the collector books sold out last Saturday.
There will be an in-store swap meet tomorrow and Sunday June 8.
Countdown's marketing manager Bridget Lamont said the cards had proven very popular since the campaign kicked off at the beginning of May.
"We've had a great response since launching them and have heard of many families committed to collecting the full set by trading cards with friends, colleagues and neighbours."