Cubita is the national brand of coffee.
It is excellent if you drink it freshly made in Cuba, but forget the tourist boxes with instant soluble Cubita coffee that you find in the tourist shops. They are cheap and the box is a nice souvenir, but the coffee is nothing special.
What to buy:
Rum is the national drink in Cuba. It is good, cheap and available everywhere.
Between the aged rums, the one I liked the most is Relicario, a cuban brand that is very difficult to find outside Cuba.
I paid 5 US$ for a bottle, but local people pay much less for it.