This is inspired by a comment I received a couple of days ago. It’s one of those questions that if you know to ask, you probably already know the answer. But I’ll say it anyway.
No, it’s not OK to staple an SD card, a compact flash card, or any other kind of flash media to an envelope, a piece of paper, or anything else.
Yes, it’s possible you’ll get away with it, as there may be some empty space inside the enclosure. But it’s also entirely possible that your staple will go right through the memory chip or the circuit board and sever or short out an electrical connection that you need in order for the device to work.
So if you must attach your digital media to something, put it in one of those plastic protective cases, then tape the case to whatever you need to secure it to.