With the purple food balls if one feels particularly heavier than others it has a particular surprise.
A second round of fast food is out in black and white checker balls. Finally they have pizzas. If it's in a foil packet it's supposed to be scented. I have a Cinnabon one that doesn't have much of a scent.
All the new balls split in half with paper packets so you can't listen for rattles so much but you can occasionally feel if something big or heavy is in there.