I'm buying things second-hand mostly. This helps a lot

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I could prepare my own food and bring it at my job but I'm too lazy for that

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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
Yes its true that you done need a branded things and buy them a cheap brand or may be you can buy them not even a brand but I mean how about if their money just enough him or her to sufficient his own things? How are they going to safe some of their money?
I've actually taken a different approach in the past couple years. Now I buy higher quality products that will last a long time. The price is more expensive, however it lasts several times longer.
For example, I got a pair leather boots on sale last year for $300. They're hand made from high quality leather. With proper care, these should last me between 10-15 years. A pair of $80 boots would probably last 2-3 years, and over time the cheaper boots would cost more due to the need to repurchase several times.
This is just an example. I know boots aren't even necessary in more tropical places, but for doing a lot of walking during a Canadian winter, they're necessary.