Do not turn off the filter. Besides the fact that it doesn't use nearly the power of the heater, your tank will go through a cycle since the nitrifying bacteria don't have any ammonia to sustain them.
Since the biggest power drain is your heater, put a sheet of styrofoam insulation under the tank, and behind the background. Locate the tank on an interior wall, they are warmer than exterior walls.
The next biggest drain is the light. Put this on a timer, you can really cut down on this if you don't have live plants. Most of my tanks get by with room light during the day, that is plenty for the fish. Tank lights in an unplanted tank are more for the benefit of the aquarist than the fish.
Buy any consumable supplies online.
Do not turn off the filter.