GAMRican saidI do bring a change of clothes, and yes it will be cooler once you get to Ezeiza. I suggest that you pack a nice new pair of pants/jeans, and a polo shirt or such for when you go through Migrations and Customs. Looking like a slob when crossing borders does not inspire confidence in the host country's officials. They will be neatly dressed. You should be too for the least probability of being subjected to a cavity search.
Have a great trip! I was in BsAs two different times for a total of five weeks earlier this year. I'm planning on going back next year for a month.
So you just change into the clothes once you get close to landing?
Yes. And, plan your clothes change time about 1.5-2 hours before landing. Once the crew starts making announcements in preparation for landing and/or any final food and beverage service begins people start heading for the lavatories and the lines start to form. You want to get ahead of that rush.
I was there in May and early June this year and the weather did get cool and wet. Think San Francisco type weather.
Some other tips...
Consider using Xoom.com to change your US$ into ARS$ (pesos). You get a great rate and don't have to change money with the arbolitos (dangerous). You pick the money up at a "More Money Transfer" store. It's safe, you will need your passport only, and the address and phone where you will be staying in Argentina. Don't use credit cards. The exchange rate will kill you. Don't change too much money when you get to the airport. Change just enough to get you into town. Use the Manuel Tienda Leon bus service to get to El Centro in town, it's the best value and costs less than a taxi and they may even take you to the door of your lodging if you are within a short distance of El Centro.
Consider using Airbnb to find inexpensive lodging. Depending upon how long you stay, a month can be as cheap as about US$800ish for a private apartamento.
Back to changing money. Don't change more than about US$300 at a time. The exchange rate fluctuates AND you don't want to end up holding a lot of pesos at the end of your trip.
Don't wear a lot of fancy clothes or you'll look like a tourist and be a possible mark for a mugging. Sportswear is popular (think Addidas track pants, polo shirts, kicks). It won't be mosquito season, but know that Dengue Fever is a public health issue.
Bring an old, worn mochila. Don't carry a fancy new bag. Clothing and other durable goods are expensive.
Do the Yellow Bus for a day. You'll get a great tour of the most popular comunas and then you can hoof it back to the places that you know you want to see more. It's worth it. Yes, it's totally tourist but again, it's worth it.
Depending upon how long you will be in BsAs, get a Sube card for the Subte (subway) and collectivos (busses). You can get one at any Correo Agentino office. Be prepared with your passport. Don't load more than about ARS$50 pesos at a time unless you want unused value at the end of your stay. Don't even think of driving in BsAs. The lines on the road are only there for decoration, and the driving, like tango...is dangerous but also beautiful.
You already speak "castellano", so you shouldn't have any problem. Just know that they speak "Rioplatense" so the pronunciation is wonderfully different. Check out the Dustin Luke YouTube videos for some insight. Also, get a copy of "Speaking Argento" and "Che Boludo" to be up on the street slang.
If you're there long enough to make some friends, see if you can go to a "milonga". These are authentic tango clubs, and not just "tango show". There are also gay milonga as well. If you do go to a tango show, La Ventana was wonderful. If you can go to some event at Teatro Colon, it will be an experience of a lifetime. It's a theatre/opera house that is only rivaled by La Scala in Italy. If you do like to dance, consider taking a few tango lessons in Texas before you go on your trip. It will be worth it.
If you're there at the end of May, the 25th is the celebration of the revolution. It's SOOOO worth it to head to Plaza de Mayo on that day. Consider wearing neutral colors or a futbol shirt of the National team. It's a very politically "colorful" event. Yes, the U.S. Dept. of State recommends staying away from such events, but if you go and smile and have fun and observe it will be amazing.
Brook Palermo is a great night club. Don't get there any earlier than 11pm. The Porteños eat late, party late and party hard.
Download a full copy of TripAdvisor to your phone. This was VERY useful. Also, there is a "Guia" app, which you can also download. No Yelp in Argentina. Check your cell phone provider to see if you can add Global Data Plan to your phone for a month. It will be VERY WELL worth it and you won't be trying to hunt for WiFi. Don't bother going the SIM card/GSM phone route if you don't have to. I have Verizon and was able to use my Samsung S3 about 30 minutes after I landed. It took about that long for the network to recognize my phone and plan, but it was worth it.
They use 220v. Make sure you use an adapter AND a converter. Beware of bringing odd appliances like hair clippers because they may not work very well (mine worked "well enough", but not "normal").
If you really want to be a great guest, bring your own toilet paper. That shit is expensive down there (no pun intended). Carrefour is the grocery that you will want to seek out for general items. Buy your fruits, vegetables, meats, and cheese from specialized stores or from street vendors (for produce). Dulce de Leche is BOMB! You will want to bring some home. Bring Ziplock bags to protect the jars on the way home.
Check out "Victoria Cream" in Palermo. It's a posteria/helateria that will amaze you. Fredo is also good for cucurucho. Coca Cola is REALLY FUCKING GOOD in Argentina. I don't usually drink soda, but it's worth it in Argentina. Also, try the pomelo soda.
Metal is precious. Your fork will bend if you push too hard. Really.
Calle Florida is a tourist trap. Beware.
Dude, BsAs is a FUCKING BLAST!!!! This is why I'm going back for another month in early 2014.
Los Argentos son muy amable y tienen passion por la vida. Disfruta!