Disclaimer: not in the EU, but have lived through some natural disasters that involved power loss for extended periods of time. So this is some kind of general advice.
If you own your home and you haven't already, do an energy audit [0]. Pay especially close attention to window and door seals. These wear out over time. You can lose a surprising amount of heat through these, and they are very inexpensive to fix. If you have ducted HVAC, check the ducts for leaks as well. Adding additional insulation if possible will also help.
Figure out what your biggest energy sinks are. In most homes the HVAC is the biggest power draw. After that you're looking at major appliances like stoves, washers and dryers, refrigerators, water heater and the like. If you can replace these with more energy efficient versions, it may be worth considering. For ones you can't, figure out ways to use them less.
Close off areas you aren't using. If you have rooms in your home/apartment that are largely unoccupied or only occasionally occupied (like a home office), close them off and consolidate into fewer rooms. If it gets especially cold, close the vents if you have ducted HVAC, seal the doors with tape and put a blanket at the bottom of the door. This will help further seal the heat into the occupied areas. But be careful that you don't cause pipes to freeze by doing this.
Stock up on foods you don't need power to cook. Shelf-stable canned goods are a good bet. It won't be gourmet, but it will keep you alive. If you are in an area that stays suitably cold throughout the winter you could use a cooler outside for food storage instead of a refrigerator.
If you have alternative means of heating (like a fireplace) go ahead and prepare to start using that a lot more. Get supplies like firewood or pellets now and, if possible, be sure you have enough to last you through the winter with increased usage. Find the lowest temperature you can tolerate at home, even if that means you may have to wear a light coat inside.
Monitor your usage regularly. If your utility provides realtime or near realtime usage information, find that now and get in the habit of checking it often. If not, figure out how to read your meter and check it at least daily.
And finally, just try to find ways to not be at home. If you can go work in an office or even a coffee shop, that's a few hours you won't have to keep your home as warm. Try to make your home just for sleeping and adjust the temperature in the home when you are away accordingly. Having a programmable/remote thermostat helps here.
[0] https://www.energy.gov/energysaver/do-it-yourself-home-energ...