Frontrunner Ms Truss has claimed there would be no new taxes or energy rationing if she became PM, as she dropped further hints about cost-of-living support this winter.
The Foreign Secretary said she is “ready to put my money where my mouth is by cutting taxes” and said her reforms would help “stave off the horror of a recession”.
Regulator Ofgem has confirmed an 80 percent rise in the energy price cap, which will mean the average household’s yearly bill will go from £1,971 to £3,549 from October.
Mr Sunak, the former Chancellor, said “we shouldn’t rule anything out” on energy rationing.
He also sought to paint himself as the candidate offering a more realistic assessment about the way to approach the economy, with tax cuts not expected immediately if he becomes leader.
Mr Sunak said leadership “starts by being straight with the country about the economic challenges”.
He went on: “My plan is the right plan to tackle inflation, to compassionately support those who most need our help and to safeguard our children’s economic inheritance.
"As Margaret Thatcher and Nigel Lawson knew, maxing out the country’s credit card is not right, it’s not responsible and it is certainly not Conservative.”
Speaking at the 12th and final leadership hustings at Wembley Arena, Ms Truss also replied “yes” when asked if she would stop smart motorways amid safety concerns.
Voting in the Tory leadership contest closes at 5pm on Friday and the winner will be announced on Monday.
Mr Johnson and his successor will then go to Balmoral for the appointment of the new prime minister, rather than Buckingham Palace.
A palace spokesman confirmed on Wednesday that either Ms Truss or Mr Sunak will be meeting the Queen in Scotland, rather than in London as is tradition.
The Queen will receive Mr Johnson on Tuesday September 6 at her Aberdeenshire home, where he will formally tender his resignation.
This will be followed by an audience with the new Tory leader, where she or he will be invited to form a government.
Liz Truss during the Tory Manchester hustings, hosted by GB News
Peter Byrne
Rishi Sunak during the Tory Manchester hustings, hosted by GB News
Peter Byrne