The Little Book of Porteño
This is the book you want to pick up to get a fast primer of Porteño Spanish. The Porteño Argentine dialect is spoken mainly in and around the areas of Buenos Aires and Montevideo. The accent and slang are very unique. They use a huge number of words that aren’t really common currency in other Spanish speaking countries, grammatically they do things a little differently, and it sounds very Italian.
If you already know some Spanish, you should be able to nail 3/4 of the material before your plane lands, or else one afternoon in a cafe in San Telmo.