Weddings.

Yes, It IS a big day. It's not such a big day that you spend your entire life savings, and have no future.

Get a DJ, get a cake, get a hall, get a photographer.......forget the doves, forget the ice sculptures, forget the wedding planner, forget the genocidial mimes, forget the big limo, keep it small. Do you really need to invite your great aunt, who you've seen 3 times in your life?

You should NOT be spending like $20,000 on a wedding.

If you're not a contractor, power tools. Buy the harbor freight version first when you need it. If you end up using it enough to break it, then you get a quality one.

Unpopular opinion but wine.

From my experience majority of people can't distinguish between 5€ wine and 500€ wine. And even if they do, they say it tastes "a bit better", not worth the 495€ difference. Pick one that tastes good to you and don't be ashamed if it's cheap.

Video games. Unless it's a game I play with friends I typically wait for it to drop in price significantly.

Apparentlyv Mr Clean MagicErasers are just melamine sponges which are actually mucho cheapo

Over the counter medications. Store brand ibuprofen, allergy meds, cold medicine, etc. Sometimes as much as 1/7th the price, just make sure the active ingredients match amounts and you're set.

College books.

pets.

Former chef: Knives. My most expensive knife is $80 with a lifetime warrantee. Most are $10-$20. Instead, learn how to use and take care of a knife.

The first round of tools for any hobby or DIY project.
If you don't know what you want from a screwdriver, snips, circular saw etc. then there is no point in buying the super primo bells & whistles expensive stuff.
Once you've used a tool and learned what you don't like about it, or what you actually use it for, or how often you actually use it... Then you can make the informed decision to just buy another cheap one, or splash out on something that's actually fun to use.

Buy the 2nd last tool you will ever need.

There are rare occasions where "buy once cry once" apply. But it's rare

Cell phones and plans. Any phone is good enough for regular use these days. And any carrier uses the towers of all the other carriers, it's not like the old days where there was CDMA vs GSM.

Wrapping paper and bows/ribbons. THey're just gonna get torn up anyway, no reason to spent a ton of money to make it fancy

Power tools. If you are not a professional and need to buy a tool (if you can't borrow one), buy the cheap one.

I used a $30 Ryobi drill for over a decade and it was fine.

Clothes and housewares. Buying secondhand is vastly cheaper, better for the environment, and can get you surprisingly high quality sometimes.

Over the counter medications. If the active ingredient is the same, delivered in the same way and in the same dosage, the effects will be the same.

Games. There's no good reason to not wait for a price drop and/or sale unless it's some multiplayer thing and you want to play with friends. In the modern day, you'll even usually get an improved product after more time has passed for patches and updates.

Wine - it is full of marketing gimmick and usually the mid range is best. The same is with whisky, rums and other alcohol.

On the other hand, at least here, is better to pay premium for craft beer.

Canned fruit salad, the ratio of ingredients is for some fuckdamn reason federally mandated so there's little difference between brands.

Possibly an unpopular opinion among parents, but: Diapers. I've noticed no negative effect on my kids when going offbrand.

Generally, medications. It's pretty rare you have some sort of specific metabolic issue which calls for the branded version; the generic is usually just as good. I have a note in my medical records to NOT give me the branded version of my meds because there's something in the expensive ones that gives me horrific reflux, while the others don't.

Most people are being very specific, but I'd say consumables in general. Rarely is a name brand food or medicine any different than generic. Often they're literally produced in the same factory. Stuff that's meant to last, generally a more expensive product will be made more durable (not always), but this isn't a consideration with consumables. If it's a one-time use or edible, I'm going with the cheapest option 99% of the time.

My default is to buy the grocery store's house brand unless I can tell the difference.

A 26 ounce can of Morton's iodized salt at my local grocery store costs $2.19. The Food Lion brand costs $0.79. Explain to me why I would pay more than twice the price for name brand salt?

Especially in goods where I know the complete chemical formula of the product like salt and sugar, until I encounter a serious problem with quality or unethical sourcing I'm not going to pay for the brand name.

Tbh about everything. Most of retail is just an industrial scale of the addage "a fool and his money will soon be parted".

Buy second hand, its fine. You probally can figure it out yourself, try to diy. Look at what people are actually doing not the brand of tool they are doing it with. Its a saw, you saw with it, you can get away with sawing a lot of stuff with the same cheap saw.

Soaps are just collections of chemicals, powerwash for example is just dish soap plus water and isopropal alcohol.

You can probably cook it at home. It will probably be better and better for you, because a pound of lard or cup or sugar looks like the red flag it is when you go to cook with it.

Your bed might be better on the floor, then on a frame.

You are probably better off walking or biking then driving.

You probably don't need to watch more shows anyways so why get fleeced to subscriptions. You probably don't need to play games as much so you can pass on that game. You probally don't need to go out for a drink. You probally don't need to go out for a meal. Etc etc

Honestly, I'm a hypocritical ass saying some of this, but its true. The urge to go spend spend spend, isn't a fluke its just successful sociol engineering to separate us fools from our money.

Newborn diapers.

Get the cheapest Walmart special you can find. Newborns don't poop or pee enough to warrant fussing over fancy diapers.

Once they get bigger and the contents start getting...bigger, then spend more on better diapers.

Mascara. There are some $6 mascaras that are way better than the $25 ones.

Not sure if this counts as cheaping out, but wait a year or so before buying computer games, when the price drops by 50% or more. Some never seem to price drop and others get really cheap right before the sequel comes out.