Keeping mementos from your travels is a tradition of sorts. Some people keep grains of sand, others buy trinkets, some save shot glasses.
We've already told you what we think of these ideas. One of our favorite suggestions is to collect "flat things," all the better to save in a journal post-trip.
Metrocards -- smart cards, transit cards, whatever you chose to call them -- fit this description nicely. They serve as an easy reminder of your time spent away from home.
Take a walk down memory lane and check out these photos of transit cards from around the world.
Correction: A previous version of the Taiwan metrocard stated that it was from Tokyo.