Have a large bottle of water for when you arrive in Cuba. Unless you are heading straight from the airport to a hotel in Havana or an all-inclusive resort in Varadero you are going to be stuck for drinking water. Make your life a little easier and take this off your immediate to do list of changing currency, negotiating taxis, finding a casa, keeping your eyes open in a new country etc. If you are arriving late at night there won’t be any stores open to sell you water or food, being prepared helps.
Bring everything you might need for your trip. Oh yes I mean everything. Cuba is a country of limited resources and what they do have is not always the best quality as they are restricted to what other countries will sell them. Plasters for a blister, birthday candles for a cake for your friend, tampons just in case, a sewing kit for when your dress breaks. These are all examples of things I needed and could not find handy but fortunately other tourists were able to help or I made do with my new Cuban attitude!