Porters carry one duffel per trekker, typically capped at 15 kg. You carry a 25–35 L daypack with water, layers, camera, documents and anything you need during the walking day.
In the duffel: sleeping bag, down jacket, spare base layers, trekking trousers, a second pair of socks per three days, toiletries, and a small dry bag for anything that must stay dry.
In the daypack: two litres of water, insulated bottle, hardshell, gloves, hat, sunscreen, sunglasses, snacks, headlamp, first-aid basics and your permits.
Left in Kathmandu: travel clothes, laptops, extra shoes, and everything you packed because you might want it. Most lodges hold a free left-luggage room, and so do we.