Any suggestions for packing and attire for BA< the Falls, Salta & Mendoza areas.

October in Argentina is a wonderfull season. It is spring. So usually the sun shines during the day and at night a fresh air is coming from the river.
But a light jacket is recomended anyway.
Enjoy it.

Was in BA, The Falls, and Salta in Sept. and most days temps were in the 70s except one Sun. it was only 55 and very windy. Salta area with mountains is warm in the day, but it cools off quickly in the evening and the mornings are cool so bring layers. The Falls were tropical so nice and warm (and humid if it rains), but wear comfortable shoes there because there is a lot of walking on cat walks and paths. It is worth every step! BA dress was more "upscale" than Salta where many were in jeans. Do see the MAMA museum in Salta if you have any interest in Inca history. It is fascinating (but closed Mondays)!!

Wise advise! Bring layers.Like an onion. t-shirts, a light sweater and a light jacket, shorts and jeans.
Su n glasses, a hat, sun lotion, and ... lipsticks. The climate is dry and sun shines
Flintstones

October is one of the best times to go to Argentina. The lowest temperature I observed was about 11C (52F). Like the other posts say, I recommend just a light jacket. In the evenings, a suit jacket will suffice. During the afternoons, shirt sleeves are enough. Enjoy!