Liz Truss says she will set out "immediate action" on energy bills during her first week in office, if she becomes the new British prime minister this week.
The foreign secretary, widely tipped to defeat rival Rishi Sunak when the Tory leadership winner is announced on Monday, has said she will be capable of making "difficult decisions" as prime minister to get the UK through the energy crisis.
There have been ever-louder calls in recent weeks that the government intervene to support the most vulnerable, with energy bills set to rise to soar this winter for the average household.
Writing in the Sunday Telegraph, Ms Truss said she would appoint a council of economic advisers to help guide her and her chancellor.
She said that she will take "immediate action" to tackle the cost-of-living crisis for families and businesses, while also delivering a "broader plan to get our economy growing, make it more resilient and make it more competitive".
"If elected, I plan within the first week of my new administration to set out our immediate action on energy bills and energy supply," she said.
"We need to take the difficult decisions to ensure we are not in this position every autumn and winter."
Recent days have been full of speculation about who could make up the cabinet in a Truss administration, with Business Secretary Kwasi Kwarteng tipped to become her chancellor.
There is also a growing expectation that the next prime minister will make an early visit to Kyiv to shore up support for Ukraine.
Johnson used his own article in the Sunday Express to reflect on his achievements, while also urging his party to come together after a summer of in-fighting.
"This is the moment for every Conservative to come together - and back that new leader wholeheartedly," he wrote.
"This is the time to put aside the disagreements of the last few weeks, fascinating though they may have been, and put the national interest first.
"As I leave Number Ten after three tough but often exhilarating years I know just how big and demanding this job is. I also know that either candidate is more than capable of delivering for the people of this country."
In what is set to be a frenzied few days for UK politics, Johnson's successor will be announced on Monday, taking over as prime minister the following day.
Johnson and his successor will go to Balmoral, rather than Buckingham Palace, for the appointment of the new prime minister on Tuesday, in a break from tradition.
The Queen will receive Johnson on Tuesday at her Aberdeenshire home, where he will formally tender his resignation.
This will be followed by an audience with the new Tory leader, where they will be invited to form a government.