I am flying to South America in November and will make an effort to include Argentina in my itinerary. I am still figuring out what's the best way, for me, to transact bitcoins. One has a choice between transporting bitcoins on one's person using physical media like a flash drive, or storing them in an online wallet. I don't want to use physical media for the same reason I don't want to carry thousands of dollars on my person.
I keep my bitcoins with an online service, coinbase.com, which provides a wide range of services in addition to the wallet (you can buy and sell bitcoin from coinbase, among other things). Coinbase enacts pretty strong security; to log in, they send a text to your mobile phone with a passcode. So in order to use coinbase in Argentina I'll need to receive texts from the U.S. I'll work out a way to do that with Google Voice or something. If not, I might use encrypted online storage like SpiderOak or Wuala. There are lots of options, which require varying degrees of technical aptitude.
Caliexpat, how do you hold and transact bitcoins?
I hold my BTC in Coinbase and BTC-e exchange. I also use Bit Stamp from time to time. I used to use Mt. Gox but just got sick and tired of the website going offline all the time, not to mention the long wait times for bank wires. I like BTC-e because I've been dabbling in Litecoin lately as well. Supposedly, Mt. Gox has plans to add LTC to their exchange at some point in the future.
When doing transactions, I meet the buyer in a public cafe with my laptop. They hand over the cash and I transfer the BTC to their wallet. We chat for a bit until the coins appear in their wallet then we part ways. I typically charge whatever the blue rate is for the day, sometimes with a small premium above blue rate. Like I said, so far I've had good success with this and have met lots of interesting people.