Finding a comfortable pack is really more important than just shaving a few more ounces off. And then you need to routinely train with it loaded, so your back and shoulders are accustomed, as well as for general conditioning. Choice of photo equip, film usage, etc is highly personal; but the most common travel mistake I see photographers making in long treks is to carry way more lenses than they really need.
It's impossible to always have the right camera and lens on hand for every hypothetical opportunity. You either have to operate on probability
or some specific hunch. Unless the facts dictate otherwise, only carry the lenses (or lens) you most instinctively use anyway. Otherwise,
enlist a mastodon to carry your gear.