At the moment, you can use the US Dollar and Euro and the Canadian Dollar in your major hotel or around the resort. Your currency can be exchanged at your hotel or in a bank for the Cuban National Peso.
The exchange rate is often better at a big resort hotel than in a Havana hotel.
Sidewalk cafe workers sell snacks for National pesos
You can buy street snacks, and cheap plastic or tin items from Peso stores, and take local bus rides. And items such as Cuban cigarettes and soap are peddled from city doorways for National pesos.
Sweets sold on the street are sold for National pesos.
Like all areas of the city of Havana, you can find locals doing work of some kind to earn extra pesos. The peanut and candy sellers pass among the crowds, while troubadors appear with guitars at any time.