Well, I keep small amount (like less than $10) of foreign currency from most counties I've visited - consider it a hobby.

In addition to Singapore dollars (primary currency), I have all currencies in the SEA country region except Philippines. List of currencies include Bhutanese ngultrum, Euro, Swiss francs, USD, AU and NZ $, Russian ruble, Georgian lari, Azeri manat, Turikish lira, South African rand, Mexican and Australian pesos, Brazilian real.

That's it so far...