If you have to take a domestic flight within Argentina, be advised that you must check your rods as baggage. You will not be allowed to hand carry them on the plane. Carrying flies on board can be a hit or miss proposition.

Also I have had more windy days than not. Sometimes extremely windy. If you can't cast in the wind then learn how before you spend your time and money for such trip. One day on a float trip the up-stream wind was so strong that the guides could not row downstream against it in a fast current. Another day the wind was blowing a floating line off the surface of the river, and I switched to a T-14 head and a sculpin pattern with great success.

Gear-wise most anything you would need for fishing in the west would be good down there.