Is it safe to carry cash for the 'dólar blue'?

Yes, but use common sense. Carry only what you need for the week and keep it in a money belt or internal pouch.

Can I use credit cards at all?

Yes, international credit cards now get a rate closer to the 'dólar blue' (MEP rate), but cash is still king for smaller vendors and hostels.

Cómo ahorrar dinero viajando de mochilero por Argentina

To save money in Argentina, avoid paying with your home bank card at ATMs or regular point-of-sale terminals to bypass high conversion fees. Instead, use the Western Union 'Cash Pickup' method or bring crisp USD bills to exchange at the 'dólar blue' rate, which effectively doubles your purchasing power.

Master the exchange rates. Do not use your standard debit card at airport ATMs. Exchange physical USD bills at 'cuevas' (unofficial exchange houses) for the 'dólar blue' rate. Check the current rate daily on sites like 'DolarHoy' to ensure you are getting a fair deal.
Book buses, not flights. Long-distance buses in Argentina are excellent and include sleeper seats and meals. Use sites like 'Plataforma 10' to compare prices, but buy at the terminal station ticket office for the best rates.
Eat the 'Menú del día'. Avoid dinner service at fancy restaurants. Look for 'menú del día' during lunch hours, which typically includes a main course, a drink, and a coffee for a set price significantly lower than ordering a la carte.
Use public transit apps. Buy a SUBE card immediately upon arrival. Do not take private taxis; use apps like Uber or Cabify for transparent pricing, or stick to the extensive bus and subte (subway) networks.

Is it safe to carry cash for the 'dólar blue'?: Yes, but use common sense. Carry only what you need for the week and keep it in a money belt or internal pouch.
Can I use credit cards at all?: Yes, international credit cards now get a rate closer to the 'dólar blue' (MEP rate), but cash is still king for smaller vendors and hostels.