I can't enlighten you on what happens when you get to South America as I've never gone past Venezuela but if you're taking the Caribbean route, the 'Bahamas and Caribbean Pilot's Guide' is a great resource.
(see:
http://http://www.sportys.com/acb/sh...Product_ID=876)
Having two things on me at each stop really helped me along on the few ferry flight's I've done through there:
1. Lots of US dollars in small denominations to pay various fees for various 'services' rendered. Almost everybody south of the Bahamas will want cash and nobody will have the correct change. By the way, these are not bribes -the invariably friendly locals will happily write you out a receipt for every dollar spent.
2. Lots of General Declaration forms -everybody will want one and nobody will have a blank form handy.