I used to wear cargos for travel, but didn't like the bulkiness. I still have a couple pair of REI hiking pants (one is convertible) and they work better but have a few zippered pockets.
Most often, I wear regular chinos. I found a pair at J Crew that I loved for the fit and comfort and went back to buy a few more pair before the style (or J Crew itself) went away. They are cotton and extremely soft and comfortable. If it's less than a 10-hour flight, I don't even bother changing on the plane. In fact, when I do change into my Nike workout pants, they are thinner and looser, but don't breathe as well.
When it gets cold, I wear a base layer under the chinos and that takes up no room in the bag but helps insulate me well.
When I look at my travel pictures from the last five years or so, I'm always wearing the same pants!