I could prepare my own food and bring it at my job but I'm too lazy for that .
I think the best step is : work remotely (digital nomad) and go live in a cheap country. In Europe it's Portugal, Lithuania etc...
SE Asia is good as well. Cambodia is providing unlimited resident visa for ~300$ a year for example and you can live there quite cheap.
That's a thing I want to experience but now I'm a young wage slave in Tokyo with an emergency fund of 500 000 yens.
Yes buying second things is helping you for your living cost, but how about if someone is being born not in a lets say a middle country or may be low. How are you going to suggest him with this condition?
another way to save money, is buying only needed things, like food, personal hygiene stuff, and nothing else
for your children you can buy un-expensive thing that don't rely on their brand, so avoid something like nike, but buy the same item under a cheap brand