I've passed one of my bad habits on to my son.  I've collected foreign currency since I was in first grade, and in the last few years I've been putting my collection in a scrapbook, with notes about when and where the money's from, and short journal entries about the trip.

My son recently started to get interested in what I was doing with the scrapbook, so we sat down and went through it.  He's been obsessed with money for a year (it was a year ago he scooped the change out of the dish at the cashier's, yelled, "MONNNEEEYYYY!!!!" and ran for the door), and he was thrilled to see that it comes in all sorts of shapes and sizes and patterns.

I gave him the extra coins that I had, obsolete and current, from euros to pesos to yen to lei, and he's keeping them in a special box.  It reminds me so much of me at his age, and gives us another activity when we travel.