Your accommodations, activities listed on the itinerary, group transportation, and 1-2 meals/day are included in your trip.
When it comes to other expenses, most places take credit cards, but in Argentina, cash is queen! This is in large part due to the parallel or "blue" market rate. You can read more about that here [link to other FAQ about money?].
Taking this into account, you'll definitely want to have pesos on hand, especially for things like taxis, tipping, and other incidentals.
It's hard for us to tell you exactly how much cash you'll want to bring to Argentina, since every traveler's budgets (and shopping needs!) are different. If you aim to use your US credit card as little as possible, we recommend bringing around USD 500 as a starting point. Don't worry, you don't have to exchange it all right away!
Keep in mind that you cannot withdraw USD from ATMs in Argentina. It's best to bring a little more cash than you think you'll need to ensure you're covered.