Most of them are suitable to be folded into origami models that can embellish an scrapbook page about your trip, or can be used as decorations.
This is one example, a simple ring that I made with Metro Cards.
The ring consists of 14 "Business Cards Simple Units". The unit is very simple to fold and assemble. I was lucky enough to get various metro cards designs, so the ring ended up being very colorful.
The instructions are available in http://www.origami-resource-center.com/business-card-ring.html. The link mentions that the units were inspired and modified from the units created by Mette Pederson, but it does not mention who created the variation. Please leave me a comment if you know the creator, so I can give him/her the proper credit.