I have a few different coins and notes from Thailand, left over from a trip there. I also have a few coins from The USA and UK which I have had for so long I don't remember how I came by them. If I come across a coin from New Zealand when I am given change I will keep it. I did consider getting rid of my small collection but one of my sons said he was interested in it.
Not particularly collect, but as everyone has said, whatever gets left over from a trip overseas, sits on the drawers forever. But I do find looking at currencies from different parts of the world very interesting. Australia has the most modern technology when it comes to printing money, which other countries are borrowing from us. For instance, I know that Canada has gotten their $100 notes printed in Australia using the polymer technology. Awesome!