Americans can not take out dollars so you will need to bring money
If you have an American bank or debit card, then you will not be in a position to take out money. It is mainly because of that entire Cuban/American embargo point. So you will will need to bring all of it with you (just hide some in a dollars pouch).
You really should bring in between $50-100/day, based on how price range or luxurious your travel style is. Take into account accommodation, meals, entertainment, taxis, tours, drinks and souvenirs. Normally bring additional considering the fact that you can not take any out. If you can, spend for accommodations beforehand on a card so you can carry much less money. P.S. the taxis add up so generally negotiate!