Most things. Clothes, cookware, phones, TV's, etc.

I would say only spend money to buy things you're passionate about. I love cooking and have spent some money on quality ingredients. Buy good spices and pans, erc. But I hardly spend money on clothing or vehicles or phones, etc.

Soap of any kind. It’s fine if you want a certain smell, but at the end of the day it all works the same. Goes for hand soap, shampoo, detergent, body wash, etc.

Free computer operating systems are great these days.

I regularly spend hours designing electronics to be cheaper. Not worse -- just cheaper. Electronic components sometimes vary in price by two orders of magnitude for the same performance, so it's worth cramming datasheets in your head as a professional or hobbyist.

For tools, I've found good midrange Chinese brands, and stuck to them. I could never afford things like Tektronix and so on.

I don't strictly require clothing to be cheap, but I do require it to be fungible -- this works out similarly though. When I find something that's good value for money and looks good, I buy a bunch and rotate them. That way I don't have to think about what to wear, and it always looks decent.

I also prefer cheap laptops. I don't need a supercomputer to work. When I do need a supercomputer, I rent one from google cloud for a few dollars an hour.

Mascara. I’ve spent $20+ dollars a few times for some high-end Sephora brands, but I’ve never thought they were any better than the $8 Maybelline I can get at the grocery store.

From my experience so far most things in life can be found cheap, moderate price and expensively priced. However there’s a point of diminishing returns on your investment ie after that point you could spend loads for marginal gains. Find this point see where on the graph you can afford it.