Eh, the problem with practicing amateur spycraft is that then you look like a spy if anyone notices.
Sure, maybe they're extremely unlikely to find an SD card in your shoe -- extremely! -- but if someone does find an SD card in your shoe, they're going to want to know why.
Just leave it in your pocket and dump it in the X-ray bin with the rest of your pocket trash. It's unlikely anyone will notice, and if they do, you're just a tourist with an SD card for your camera. Maybe they throw it away, maybe they copy it, but it's unlikely to end with you spending four hours being questioned about why it was in your shoe.
Could put a micro SD card in a SIM card slot in your phone maybe.