Recruitment freezes, IT programmes, consultancy and transport are among the areas being tackled to help cut the deficit.
Chancellor George Osborne has been laying out the immediate plans which he says will save the country £6.25bn.
Standing alongside his Lib Dem deputy at the Treasury, David Laws, he said the reductions would be made while maintaining "frontline" services in key areas like the NHS.
Schools spending is also being protected along with funding for Sure Start programmes.
Some £500 million will be "recycled" to boost employment and skills, and the rest will be used to cut the Government's debt.
The savings were based on "strong economic advice" from the Bank of England and the Treasury in favour of "early action to deal with our debt", the Chancellor said.
Mr Osborne said the savings would include:
:: More than £1 billion of "discretionary" spending such as consultancy and travel;
:: Nearly £2 billion from IT programmes, suppliers and property;
:: Over £700 million from "restraining recruitment" and cutting quangos.
:: More than £500 million from cutting "low-value spending".
Referring to a note left by outgoing Labour chief secretary Liam Byrne for Mr Laws, Mr Osborne said: "It's all very well writing a letter telling us the money has run out; the real challenge is having an answer to that letter."
He said his theme of "we're all in this together" meant "cutting wasteful spending while protecting the quality of key frontline public services we all depend on".
