

The first coin I can remember definitively buying for numismatic purposes, a humble little 1700 William III halfpenny. I'm actually not sure if it was that one or one of my George II halfpennies, but these coins were a cheap way to hold a part of the past 300+ years ago in your palm.
If we're talking about the first coin that came into my possession that I still have, it's probably one of the British and British colonial coins a relative who was a non-serious collector offloaded to my family, that I then took an interest in (this was about five years ago).