An apple- what sort of a craving is that?!?! LOL! Only kidding!
Seriously, as the others have suggested- get busy, drink a glass of water, do something with your hands, distract yourself- it's only a craving- your body doesn't need the apple- it's getting all it needs from your shakes. It will pass...we've all been there, hold tight, you'll soon be in ketosis and not want to eat!