If you dont bring US dollars you will end up paying twice as much as you should. When first told about the tour of angel falls I was told US$190. However because I only had boliviars I ended up paying $387.
Being unaware of this can screw your budget as it did me.
When I am on holidays like to send my friends post card form the most remote location possible and would have liked to send one from Canaima. At the airport the are post cards for sale, there is a post box, but no one sells postage stamps, I asked and was told buy them in Ciudad Bolivar. So unfortunately no one got a post card from Caniama - so the tip come prepared.