Rolling luggage is amazing, especially that that goes into the overhead compartment.
"I bring a week's worth of thin clothes that layer. If I need more, I'm either washing by hand or using a service. Basic toiletries, an e-reader, phone, keys, charger bricks, a notebook/pens, daypack. It fits into an underseat backpack with room to spare."
That's if you don't need to take more or heavier clothes, formal clothes, an extra pair of shoes, if you're packing gifts, or extra gear taken space elsewhere (e.g. camera and lenses in your backpack), and not taking stuff like souvenirs and such back.
>This has scaled fine all the way up to multi-month scientific expeditions in remote locations.
If you slob it like a 19 year old backpacker, sure.