Pack the absolute minimum. If you really need something, you can almost always buy it wherever you are going. Even trekking in the deep Himalayas, there was always a spot to buy an extra t-shirt or socks every day or so.
That was back when flights included two free checked items.
On my second trip to Europe one of my suitcases was full of T-shirt swag to give out at a conference. Lugging both up the stairs, across the train tracks, and back down was a hassle.
Both of these were over 20 years ago.
And then there's the story at https://notalwaysright.com/a-steam-powered-cruise/392530/ of a couple trying to bring a full-size espresso machine on their cruise, so they can have their special coffee.
Totally understandable! Amazing wine - I didn't want to leave Constantia. But I picked myself up and dragged myself to Stellenbosch !
And at the end of the trip, I didn't want to return home. Such an incredible country that still holds a very special place in my heart
I didn't.
Things were a lot looser then. I brought a 6-pack of Negra Modelo as carry-on for a trip to Europe. The airport x-ray staff in Albuquerque recognized it on the screen, which impressed me. They had no problem with it.
As an aside, you should absolutely wash your clothes after buying them before wearing them. They're covered in chemicals that aren't great for your skin. I usually pack a week's worth of clothes and do laundry once a week while traveling. Doing laundry more often is a drag.
My favorite way of traveling involves a 20l backpack and a small checked bag. There is usually enough space for whatever I need, I don't have to worry about overhead space, and I don't need special travel versions of the things I use. But sometimes I take a larger (~100l) suitcase, or even both for longer trips with multiple activities.
As for trekking in the Himalayas, you should always carry clothes you don't expect to need and gear you hope you won't need. Mountains are objectively dangerous, and bad things do happen occasionally. Such as the unexpected blizzard on the eastern side of Everest last weekend.
Bulky gifts.
Bulky sports equipment.
Lots of kids' clothes. Kids' toys. Kids' books. Kids' medical kit.
Clothes that span multiple seasons or climatic zones: warm, cold, heavy rain, snow. Extra shoes. Especially when you know that your things will get wet and that you will have only occasional opportunities to dry them.
Suit/dress/fancy shoes if going to a wedding or other formal event.
Add that, and 80L is not much volume...