Back in December, two of Gavin Thompson's friends issued him a challenge: See how far he could stretch $150 for charity.

Challenge accepted, the frugal Ottawa mathematician set to work, and by the time he was done, he had multiplied the original sum by 10.

Here's one of Gavin Thompson's receipts, which says he managed to save more than $900. (CBC News)

"You really need to work points programs and coupons, and [buy] end-of-season stuff, especially," said Thompson, who wrapped up his challenge this week and discovered he had turned that initial $150 into more than $1,500 worth of goods for two local organizations.

The vast majority of the items Thompson procured during the challenge — coffee, canned food, toothpaste and other toiletries — went to two local charities: the Gloucester Emergency Food Cupboard and the Youville Centre.

Thompson told CBC Ottawa it's really not hard to replicate his formula for getting the best deals from major chain stores.

The Youville Centre's Heather Heagney says Gavin Thompson is 'just so passionate about what he does.' (Stu Mills/CBC)

Pharmacies, for instance, are often jammed with merchandise and don't have much floor space to keep slow-selling products on the shelves, Thompson said. So they mark them down and try to unload them at a deep discount.

He also keeps a mental note of the best-before dates on key items he saw in stores, returning to grab them when they're at their lowest price.

"A case of baby formula is $27 to $30. When it's come close to, say, a month left, they'll sell it to you for $3 sometimes. Three dollars a case? I'll buy it all. Some charity needs it," said Thompson.

There are also points programs.

"I've had situations before when I've walked out of stores with hundreds of dollars worth of chocolate bars," he said.

"And when you factor the points back into it, they've paid me $30 to leave with [those] chocolate bars."

'He's just so passionate'

Thompson has been buying discounted items for the Youville Centre — a local non-profit for adolescent mothers and their children — for the better part of a year, said Heather Heagney, who oversees communications and community development at the agency.

"He's really taken the time to look at our list of needed items for the young moms and the babies. He''ll consult with us even before he goes shopping," said Heagney.

"He's just so passionate about what he does. It's just very admirable to us that he takes the time and the effort."

As for Thompson, he acknowledges that talking about his shopping strategies might clue in the retail chains he deals with, but says spreading the word's worth it.

"I'm hoping other people will pick this up and challenge themselves," said Thompson.

"It's a way to give things back to people who need it more than we do."