CUC vs Cuban peso (MN) for tourist use in Cuba

I have read that it is wise to have some cuban pesos to buy food from street vendors and drinks. I'm confused. Can tourists only buy groceries and other such things in CUC's? Or can we use both depending on the place of business? Help leaving soon!

Answer: by Vic Webmaster Havana-guide.com

The normal procedure is that tourists can only pay
in CUC (Peso Convertible), as a matter of fact, the CUC is a replacement for the USD ( USD was only accepted before 2004). The Cuban citizens have their "own money" for internal use, the Peso Cubano, or also named Peso Nacional or Moneda Nacional (MN).
In most shops, shopping malls, bars, street shops they will ask you for a payment in CUC, that is considered as hard currency. Therefore the shops, shopping malls etc. are called "Dollar Shops" by the Cubans because they only accept CUC even from Cubans. On the streets and in street markets, they will always try to get paid in CUC, because the Cubans are paid in Moneda Nacional by the government, to them the CUC has more value. You may find some exceptions on the streets, but...consider this, as a tourist you don't know what the real price or value is, in the street markets, you can't hide that you're a tourist and when you insist to pay in Moneda Nacional, be sure that you will pay more. My advise is forget the Moneda National and stick to the CUC, that's the simplest and watch out for the classic tricks of short changing and mixing CUC banknotes with Moneda Nacional banknotes (a 1 to 24 ratio) further reading:
Money in Cuba