Buying and selling gold coins where I live in Scotland is pretty darned difficult, (try to barter with a Gold Coin in the USA may well get you arrested and I've heard that many places won't even break a $100 bill) you might be better off with a prepaid VISA card although in some parts of the world such as Cyprus there might be a daily limit you can withdraw. If you are going to have some currency then American Dollars aren't what they used to be as currency for world wide acceptance, especially with the easier counterfeiting compared with UK Sterling.

When operating in countries with endemic drugs production there probably will be folks who will have access to local HSBC/Wells Fargo banking facilities.