Cell Phone Wallet
This is a silicone "cell phone wallet". You peel off the paper on the back and it sticks to the back of your cell phone. You can put credit cards, hotel room keys, business cards, or whatever in it.
I have an Apple 6Plus (the big one), so you can see about what size it is when it's on the phone.
Actual dimensions are 3.5 inches long and 2 inches wide.