Strawberry Milk Candy

Spoiler Warning: Spoilers for RobiHachi may follow.

Yang holding a bag of strawberry milk candy.

Strawberry milk candy (みるくいちご, miruku ichigo lit. "milk strawberry") is a type of candy with crispy filling favored by Yang, who throughout the show is very often depicted eating it, despite admitting he's not a big fan of strawberries, milk, nor candy (though he doesn't hate them either). He eats it because he has very fond memories linked to them, namely Robby giving him a bag when he came to ask for more money.
Anime episodes only make it seem like Yang is constantly eating from one and the same bag, and him running out of candy in it also symbolizes the end of his infatuation with Robby (or at least him giving up on pursuing this dream), but the drama tracks reveal Allo and Gras are, in fact, in charge of constantly replenishing the stock of candy, which means he is not eating from the original bag anymore, or at least had it refilled.
Yang eating this type of candy is a nod to another character played by his Japanese voice actor, Tomokazu Sugita: Gintoki Sakata from Gintama (also directed by Shinji Takamatsu). Gintoki is also a fan of strawberry milk.