Shut off every other light that you can get away with. Same with elevators, escalators, etc. Shut off computers at night. Close blinds wherever there is direct sunlight coming in during the warm months. Open blinds wherever there is direct sunlight coming in during the cold months.
Offer 32-hour work weeks and the associated salary cuts; some people would love to work less and can adjust personal spending to make due with the pay reduction.
Cover roof tops with two-sided panels, one side black, one white; then flip them during the appropriate seasons to save HVAC costs.
Stop selling off government cars that are only a few years old; one should be able to get 2 or 3 times the amount of service from a car even if it does require a repair now and again (this is what successful companies already do!).
Reduce garbage/recycling collection to every other day.
When assigning road construction, make the contract provide the government a 10-year warranty and the contractor provide a hefty deposit that he gets back after the warranty is up.
Consider permanently using open source software tools where possible, and use open file formats so the government is never locked into a vendor.