It's one for each of their nationalities/culture, maybe? Pretzels for Medic, Baguette for Spy, English Muffin for Demo (close enough), the Russian bread, ration for Solly, cornbread for Engi, Cinnamon Bread for Pyro (sweets), toast for Scout (?), and maybe the other bread for Sniper?
Called it when they announced Portal for Shield. Just knew they had to do this as well. However, I'm not sure how playable it would be, considering it's a five-inch screen. Well, it is a controller, too, so there's that.