What to pack

The logistics of living out of a backpack for a few months can be a bit daunting. I’ve been spending a lot of time researching what things I should get before I leave, what I should bring that I already own, and what I can and should pick up along the way. Given that I’ll be trekking high up in the Himalayas, braving the Indian monsoon, and lounging on Thai beaches, I’m going to need versatile clothing and gear that can stand up to all these weather extremities. That said, I’ve been doing hours and hours of research on specific types of items such as pack covers, trekking pants, waterproof jackets, etc. Right now I’m unsure whether to get a down sweater or stick to a soft-shell jacket to serve as a mid-layer. Any thoughts?