I lost my wallet and was just about to head out to buy one when I reminded myself that I should just design a new one. Sure, there's a glut of slim wallets out there, but I wanted to put my own take on it. It works really well with 5-6 credit card sized items and has a separate slot made for easy access to a MetroCard which saved me from missing a train the other day.
There's a little nib that clicks into the small hole toward the top of the card. Hopefully, the MTA won't change the card design any time soon.
If you aren't in NYC, you can still you that slot for a picture of a loved one or yourself, if you're into that kind of thing.