First determine the range you want when loaded and the range you want unloaded. It may well be, like others have said, that with a 9 X 3 set up, you can accommodate both ranges without changing the system at all. You simply won't use your top gears when touring or your low gears when not touring.
For my part, I have a very wide range in my rear gearing, thanks to my IGH. It's wide enough that I seldom moved between the two chainrings on my compact double up front. I ended up removing the front derailer entirely. When I load the bike up for a trip, I manually move the chain down to the smaller ring. When I come back, I move it back to the big ring. It's effectively two sets of gearing, one for loaded riding and one for unloaded, but it requires no swapping of chainrings or gear clusters.
With a 9 X 3 set up, I would think you could get a wide enough overall range that you could accomplish the same thing just by staying off the big chainring when touring and staying off the small one when not touring. Just think of it as two, separate, 9 X 2 set ups. You can even play with the limit screws on your front derailer if you want to lock yourself out of the upper/lower ends of range, but that seems like more trouble than it's worth. But then by not having a front derailer on my bike, I find that by locking myself out of my lowest gears when unloaded, I have an easier transition to loaded with lower gears when I do go on a trip.