How should I pack so the porter can carry my stuff?
Generally, porters would use your backpack or bag. But they can also bundle multiple bags together. Ideally a waterproof duffel bag would be best. You can find them pretty reasonably priced in the Thamel area of Kathmandu if you don't have a suitable bag. Especially if you are trekking between April and early October pack anything you definitely needed to stay dry in a plastic or waterproof bag. You will probably want a small day pack to carry anything you want accessible to you while trekking.