I never had any issue with any cocktails that I had in Cuba. The components are generally all bottled items anyway. Hotel Nacional has one of the best mojitos in Havana. Stick to bottled water for regular drinking. Food quality varies but, I ate from the cafeterias (lunch windows) many times without any issues. If you are going to eat any meat though, I would stick to a decent restaurant or paladar, if you go to a market, you realize how variable in sanitation the meat handling can be.
While I was in Varadero, I had no issues with food or drink. Same policy though, don't drink the water.