The benefit of packing light really can’t be overemphasized. The measure of a very good traveler is in fact how light she or he travels.
Just to start, much of travelling in Europe and the third world is called backpacking. They don’t stay in tents, they just carry everything in a backpack. There are lots of great videos on YouTube about preparations and packing. Some are specific to the area, such as Packing for a backpack trip to Honduras etc. Also Google packing lightweight for world travel and there is an entire book that you can download by chapter.
The main thing is that travelling light is very freeing. You are not tied to a suitcase. You can enjoy a mile long walk to the bus station. You can move quickly between modes of transportation, walking, to bus, to train, etc. Even in big cities you may walk from one subway line to another.
The lightweight synthetic materials are easy to wash and dry overnight.
It’s better to take less that more. Anything you really need you can buy but we are reluctant to throw away stuff, especially when for example you brought two pairs of long pants but only need one. You don’t want to throw away your good pants you had altered for length.
I use a duffel bag. The key is to lay your cloths out, fold them neatly, and pack them on top of each other.
I remember years ago I was about to go on a ski trip. I had a suit case packed with my cloths, then said screw it, I’m going to stuff everything into my duffel bag. It all fit and I haven’t looked back since.
Most hotels have a washer/dryer, and they’re moving in the direction of having a small store next to the front desk instead of room service.
I basically carry the duffel bag, and a small back pack for my electronics. On the plane, my duffel bag goes over head, which leave all the electronics with me (Bose QC-15 headphones and a mini laptop).