(1) Reduce the influence of lobbies over the political process. They manipulate public policy for private benefit, and are thus collecting economic rent at the expense of everyone else.
Moderate liberals like myself strongly support this. However, these lobbies exist on multiple fronts: including fronts that liberals support. Examples: gun lobby, aerospace/defence lobby, private for-profit education lobby, healthcare lobby, healthcare insurance lobby, professional unions, etc.
(2) Improve efficiency in public organizations.
People who work for the government should ensure that every hour they pour in translates to real work done for the government. You need strong managers to trim the fat and improve throughput.
(3) Reduce the amount of money paid out of the public purse to contractors.
Again, when the money is not mine, but I am in charge of disbursing it, I tend to be less cautious. Public procurement is known to be a good source of money if you can latch onto a good sub-budget with more money than it needs. Budget-managers in government hate reducing their budgets, because it gives them less power, and less leeway in the future when they need more. Asking for budget increases is like pulling teeth, so why would you voluntarily cut your own budget? What if you need to increase it in the future?
(4) Fix market failures (externalities).
As an economist you know what these are: smoking causes harm beyond the buyer and seller, vaccines cause benefit beyond the buyer and seller, proper-education, etc. This is simply improving economic efficiency: it's not "big government" and "regulating everything".
(5) Use government money for very-long-term investments. Such as bridges, dams, power plants, power cables, etc. Private companies require massive discount rates to assume such risks, but the government can support such projects at the long-term Treasury bond yield (very low interest rate!).
(6) Use private companies to exploit competition and gain more efficiencies. An example: government builds the roads, private companies compete by offering bus routes to consumers. The government is not as good at selling groceries, operating bus routes, etc.
