Not really a trick, but would be a good opener for tricks with a mini deck. Place a regular card on top of the mini deck. Ask them if they want to see a little card trick. Take out the "regular" deck. Say something along the lines of, oh, that's a regular card trick, I wanted to show you a little card trick. Palm the card and show the change.
I have no idea how well that would play out as I just made it up now.