To add to Ken: US bank and credit cards won’t work. The two banking systems don’t communicate. Bring enough cash to cover a hospitalization emergency.
Wifi is available at hotels and you can buy data cards to use at your hotel or hotspots. Otherwise, your phone won’t work.
There is still a daily flight to Santiago de Cuba at the eastern end of the island despite the US restrictions on all flights except to Havana.
If you go to the eastern part of the island, it’s poorer. In Guantanamo City people on the street were asking for skin cream and ballpoint pens. I wish I had brought the little bottles of cream from the hotel and pens to give away. Simple enough for us to do.