One bag travel

There are variables to consider. Will you be able to wash things in a tub/sink? You can take much less this way. Just wear the shoes that you wear in the plane. A pair of pants beyond what you wear in the plane. Shorts that match both pants. I wear nice, quality wool socks. I can wear them for more than one day.

I just spent a week on a river trip, and everything I took (including the boat) would fit in a checked bag. How big of a bag do you plan to take? I have also flown with a personal item only for a three day trip. How much do you really need to take?

For me, it depends on where I am going exactly. For example, I rarely bring more than a single pair of shoes, unless I'm expecting to go somewhere formal or sandy. One set of clothes per day is usually enough, unless I'm expecting adverse conditions or laundry access. As far as space vs weight, space is fixed by the bag whereas weight is limited by what I can carry and for how long.

Just running through the days and any plans you know of should help, taking the expected climate into consideration for quantity of spares.