Mr Stewart said the supermarkets were on to a good thing, but they did not need to ditch plastic bags altogether.
"I've been through the whole thing. There are options out there."
Mr Stewart said the store also offered paper bags and jute bags but most people did not want to spend extra on paper bags.
Countdown's managing director, Dave Chambers, said now was the right time to take the lead.
"We have been tracking customer sentiment for two years and our most recent research, concluded in August, indicates that 83 per cent of our customers support phasing out single-use plastic carrier bags," he said.
Mr Chambers said customers adapted quickly.
"We're confident Kiwis will get in behind this change across the country, and we're committed to making the move from check-out bags as simple for customers as we can."
Charging customers for plastic bags was considered, but rejected, Mr Chambers said.