When we went we found that US dollars were readily accepted by shops and market sellers etc. In fact in some countries they preferred it to their own currency. However if you want to do anything official, visit a museum, go on public transport etc, then you need local currency. We took a small amount for countries like Brazil, Chile. Uruguay etc, but you can change US dollars quite happily at banks and money change outlets. Often the rate of exchange for cash was better than we would have got at home. Bermuda/Jamaica etc, no problem at all with US dollars anywhere.