Saving, not spending, will dominate Wednesday's agenda. And one of the biggest savings could be a public sector pay freeze. It would be hugely controversial. Media leaks last week claimed Mr Sunak wants a freeze for everyone except frontline NHS staff.
That won't go down well with the police, teachers, civil servants or anyone who thinks they've done their bit to ensure the public sector keeps going in tough times. Even a return to a 1% cap is likely to be fiercely resisted.
Some commentators think the media reports were Treasury kite-flying. Even so, in the summer, Mr Sunak suggested that as private sector pay had taken a huge hit, in the "interest of fairness" the public sector's 5.4 million workers should share some pain.
Trouble is, relative to pay in the private sector, public sector pay has fallen to its lowest level in decades, according to the IFS.
Only during the pandemic has public sector pay performed more strongly than in the private sector. Union leaders have already warned of industrial action to ensure members' pay does not fall further behind.
3. 'Levelling up'
Many promises have been thrown off-course because of the pandemic, and the government will be keen to get its north-south levelling up agenda back on track as soon as possible. Infrastructure spending is key to this.
The north has long complained that the Treasury methodology used to calculate the cost-benefit of spending money on big projects is inherently biased towards London and the rest of the south east. So, expect some changes to these calculations. And watch out for whether any spending promises are new money, or simply projects brought forward.
To underline his commitment to spend on big long-term projects, there is talk that Mr Sunak could publish details of a National Infrastructure Strategy and a Research and Development Strategy.
And in a symbolic move that levelling up is more than a question of infrastructure, the Financial Times has reported that the chancellor could also announce that parts of government could relocate from the capital - with the Treasury leading the way.
4. What happens next?
While Wednesday will be about spending and borrowing, at some point the chancellor will have to decide how it will be paid for. He will start to address this in next March's Budget, although most economic commentators feel the economy will still be too fragile for major tax rises.
It is possible that, with the success of a Covid vaccine, the economy could bounce back, limiting the need for big rises. However, Paul Johnson, director of the IFS, told the BBC that four or five years down the road he still expects the economy to be about 4%-5% smaller than before the pandemic.
Rein in spending and raise taxes too early, and recovery will be choked off. Leave it too late, and the public finances will spin out of control.
"It's a fine judgement," said Mr Johnson. Both the chancellor and Prime Minister Boris Johnson have, however, said they don't want a return to austerity.
There have been reports the Treasury could raise money from changes to Capital Gains Tax, pensions relief or self-employment taxes. But this is tinkering.
Mr Johnson believes £40bn of tax rises are necessary over the short-term, and that sort of money cannot be raised without touching the Big Three: income tax, VAT or national insurance. These bring in almost two-thirds of government revenue.