Speaking to the Business 4 Life coalition of suppliers who support the government's Change 4 Life initiative, Johnson said smaller snacks should be available in places where people make impulse buys, such as c-stores.
While many companies offer smaller sizes, they are often available only in multipacks, he said.
"We were raised to waste not, want not, so if we buy a big chocolate bar, we'll eat it all," Johnson said. "If snack sizes were available it would help us to eat less."
The minister also challenged manufacturers to create healthier snack choices. "That's not just good for the nation's health - it's also good for business," he said.
The Business 4 Life coalition, which includes Mars, Coca-Cola, Britvic and Nestlé, has committed £200m to the Change 4 Life campaign over the next four years.