I just stumbled on this community randomly, but I'm so glad I did. Thanks for all the great content, I hope this will blow up :)
https://interestingengineering.com/innovation/an-ingenious-diy-heater-for-7-could-keep-homeless-people-warm
In the same vein as keeping your freezer full/putting bricks in it make it consume less energy.
Keeping your freezer full does keep the temperature more stable, at least.