If you have never been to Cuba you might be astonished what the situation is like. When I got advice from a Cuban friend, what they told me, I could not understand to bring food, cosmetics and toiletries.
Things work much different there and I realized at arrival, things are very slow, and there are cues just to buy bread for example. Supermarkets seem like a jewellery shop. High prices and sparsely stocked stores. Bring at least some basic medications, favourite snacks and cosmetics from home. Bottled water is essential to buy whenever you can find big bottles. They come in 1.5 litres compared to the smaller ones 0.5 liters.
I will not add clothes since it is up to each individual, Cuba is a tropical island with high humidity during rainy season.
medication / ibuprofen, antihistamine, betadine, Imodium,
toiletries / toothpaste and toothbrush, deodorant, dental floss, toilet paper, razor blades, deodorant, shampoo, body wash, hand sanitizer, tampons, insect repellent, sunscreen. bring some tissues and toilet paper since this is scarce in Cuba.
food / whatever favourites you got, you will not find it easily in Cuba and if you will, it will be about triple the price. I suggest nuts, dried fruits.
Others / Water bottle, flip flops, outlet adapter, sandals, hiking boots
Most Important is to bring USD Cash or better Euro , The Euro gets a much better exchange rate, US credit cards are not accepted at Cuban ATMs