I'm 19 and just starting my foreign and historical collection, but I've inherited and found a few neat things. At most right now I have some old brit pence from the early 1900's and American bills for states money. The 1 and 2 dollar bills from Canada that mum saved for me and my siblings are fun for sure though :)

Also, there are stores that have you buying foreign money, as far as I remember, Investors group relies on the fluctuations of currencies US versus Canada, or Canadian dollars against Chinese yen, the yen goes down, and some of the investment is switched to it, then the yen goes up and is switched back at a small but noticeable profit.