Here is what you have to do as a tourist. If you don't do this, you will pay almost double for everything:
SEND YOURSELF CASH VIA WESTERN UNION. Pick it up at any of the many Western Union pick up points, showing your passport. DONE.
OR
Bring PHYSICAL DOLLARS and swap them at black market exchange places (called cuevas) in Florida street in Buenos Aires. This is not as scary as it sounds, it's like going to any other money changer and scams are not common provided that you inform yourself on the rate you should be getting beforehand.
If you do not do this as a foreigner with no Argentine bank account, and you swap money at 'legal' exchange places or pay with your foreign debit or credit cards, you will be given the official exchange rate, which is much lower. As of right now, 1 dollar at the official rate is 99 pesos, while sending money to yourself via Western Union or swapping at a cueva is minimum 185.
So you DO have to use cash, but it's a small inconvenience to pay for getting a 50% discount on everything.