Two days later, he popped open one of the packs, only to discover the chocolate coating was golden.
Thinking they were inedible, a disappointed Wayne brought the biscuits to his partner, Rose, to see what she thought.
"She opened up the packet and there's something wrong with them," he said.
After reading the promotional material on the packet and discovering the accompanying golden ticket, Rose asked him if he'd kept his receipt, suspecting the strange-looking Tim Tam biscuits may just be a genie in disguise.
And indeed they were.
Every year, biscuit tycoon Arnott's scatters three packets of golden Tim Tam biscuits across Australia and New Zealand, with the promise of granting three wishes up to the value of $100,000 to whoever purchases and discovers one of the packets during the campaign period.
"To be quite honest I knew nothing about it," Wayne said, of the Wishes' campaign.
Wayne is the only person to have discovered the golden Tim Tam biscuits in this year's Australasia campaign, and the second person from the South Island ever to have won; a North Canterbury family discovered a pack of golden of golden Tim Tam biscuits in 2019.
"It's very humbling," McDonald said.
"We sat there in shock for about five minutes after we found out we'd won."
McDonald, a fitter welder by trade, was left unable to work for 12 years after suffering a spinal injury, and has only recently rejoined the workforce.
He has already planned what he would like to do with his three wishes, claiming he's going to buy four second-hand Harley Davidson motorbikes, a new car and then deposit what's left into savings.
He and Rose have no intention of taste-testing the golden Tim Tam biscuits, despite the paint being perfectly edible.
Instead they plan to find a way to preserve the biscuits before encasing them in epoxy resin, where they'll remain golden and glinting for years to come.
Arnott's brand manager Michelle Kitchen said there was no denying the love Kiwis had for Tim Tam biscuits - New Zealanders enjoyed over 65 million of them last year.
"We were excited to hear about Wayne discovering one of the three golden packs of Tim Tam in Ashburton and we hope he enjoys his $100,000 prize. What more could you wish for?
The campaign ended on July 4, and McDonald remained the only prizewinner.
Starnews.co.nz