The line-ups extended out the door, as customers battled the elements outside three of the restaurants in Conception Bay South and Paradise.
Money from the sandwich sales will be donated to the family of Riley Mercer.
Mercer, 15, was diagnosed with a rare form of brain cancer in December 2011.
The tumour has left Riley unable to communicate, and in recent months, his condition has worsened. The teen has lost his sight and hearing, and is now confined to his bed.
This is not the first time the Mercer family has experienced unthinkable hardship. Riley's sister, Alex, died of a similar cancer more than a decade ago.
Their mother, Louise Mercer, said she never expected so much support from Wednesday's fundraiser.
"It's overwhelming... I really don't know where it all came from... but it's overwhelming and it's certainly inspirational. You know, it keeps us going. It keeps us fighting for Riley," she said.
"Before you know, we were spelling on a board or spelling on his chest. He may get a letter or two now, but he doesn't really get the whole word, so there is really no way of telling Riley what's going on... but we'll be sure to tell him once he's better."
Peter Bugden is one of the three Mary Brown's franchise owners.
He doesn't have a final count on Wednesday's event, but he's guessing the effort raised between $25,000 and $30,000.
Bugden said meeting Riley's mom put it all in perspective.
"When you realize what she is going through, it really makes you realize, 'Oh we're here and this is hard today, but it's one day for us — but for them, it's a lifetime.' It really makes you stop to think," Bugden said.
Karen Nash took time out of her day on Wednesday to buy a sandwich and support the family.
"It's just a great cause. It's a little boy who is stronger than anyone here. So how can we complain about standing in a line-up for an hour just to give a little bit of support," she said.
Last month, Villa Nova Junior High School in C.B.S. raised more than $14,000 to help support the Mercer family while Riley's parents stay by his side.
A hockey tournament fundraiser is being planned in Riley's honour, to be held at the end of November.