Fashion accessories. For most fashion (not workwear), the expensive stuff is made from the same material and in the same factories as the cheap stuff, they just market it harder.

Body wash. It's watered-down soap. Just buy a bar of soap.

Amazon Prime. Amazon used to be space-age Sears. Now it's just Aliexpress. Fake reviews and bribery are rampant, dangerously nonfunctional products get top recommendations, used and broken products get resold as new while untouched returns get thrown into landfills, Amazon Basics violates IP, and they're putting ads in Prime Video now.

Microwaves and space heaters. The boxes may try to convince you otherwise, but the amount of heat these devices can deliver is bottlenecked by the power outlet. Every 1100W microwave is just as effective as the others. If you're paying more, it's for looks and for features you'll never use like popcorn mode.

Electronics, for most people. Most people won't get more use out of a new $1500 phone than a last-gen model from the same manufacturer for $500. Do you really want a $200 smart coffee maker, or a $20 dumb coffee maker with a $10 plug-in timer?

Software. Obligatory FOSS plug. I don't blame people for sticking to what's familiar, but if you have the time and energy to spare tinkering, most software out there has a good free or open-source equivalent these days. At least for personal use. In my use case, LibreOffice beats Microsoft Word, Photopea beats Photoshop, and Google Sheets beats Excel.