Obviously, I have to do a little pre-trip research before we leave to make sure I know what I’m after. The best part is in Vietnam I will be collecting DONG! Giggle away my little minions; that’s funny as hell!The exchange rate is approximately 20,000 Vietnamese Dong to $1US. I think it’ll be crazy to be paying for items with 50,000₫ notes. (That’s only about $2.50.) Also try wrapping your head around being able to take out a maximum of 2,000,000₫ from a bank machine. Apparently, that’s the machine limit. (That’s about $95!)
The least valued currency for exchange alternated between the Zimbabwean Dollar and the Vietnamese Dong for a while. Now the least valued currency is that of Somalia with the Vietnamese Dong running 2nd. Thanks VietnamWiki for the photo. 
The Cambodian Riel is approximately 4010៛ to $1US. Unlucky for me the coins are rarely used. That could be a bit of a struggle collecting them. The Thai Baht is about 30฿ to $1US. Gotta love travelling with exchange rates like that. It definitely helps the bank account!
FYI: All of this learning, and now I know a lot of currencies are actually descendants of the Spanish Pieces of 8. How very Piratey! Arrrr!