What are some countries where USD is unofficially used a lot?

Some countries use US dollars as an official currency, like Panama - that’s different.

And at major tourist sites vendors will often accept US dollars, pounds, euros, etc - also different

Which countries have you seen US dollars used in for routine transactions even though it isn’t the national currency? Where you were surprised at how much people used or accepted USD?

I was surprised by this in Argentina or Tanzania. You might get a better price in the local currency (and the blue rate is another factor here) but not necessarily, and in general I was surprised at how much dollars were used.