I could recycled them which would probably be the easiest thing to do. But I thought of another use for them. I had a business card holder that wasn't being used for anything. I don't know about you but I have a tough time keeping track of all the username and passwords that I have. And you know that experts recommend that you don't use the same username and password for all the websites you are subscribed to.
If your card is blank on the other side, you can write the website name, your username and password then store it in the business card holder. I keep them in alphabetical order by website name but you group them any way that is easiest for you as a reference. Keep it in your laptop bag or by your computer so they are always on hand.
Bonus: You are recycling and being organized too.