C-3PO's was a cereal product, brown and rectangular in shape, that prominently displayed the image of the protocol droid C-3PO on its packaging. The protocol droid himself is credited with giving the cereal its name.
During the time period of 15 BBY, the Sith Lord Darth Vader employed the Force to levitate and serve a bowl of the cereal to his son, Luke Skywalker, after Skywalker voiced his displeasure with the scrambled eggs and bacon Vader had prepared. This meal between the two Humans took place at Skywalker's residence within the Lars homestead situated on the planet Tatooine.
On occasion, C-3PO and R2-D2 would carry boxes of this cereal with them during their travels. In one instance, while under intense enemy fire on a desert plain, the droids sought refuge in a cave where they shared the cereal with a friendly alien. Later, after becoming lost in a rocky terrain, the droids encountered a rock-like alien who discharged a blaster in their direction. Subsequently, this alien requested food in a language understood by the protocol droid. Threepio offered the alien a bowl of C-3PO's cereal, which the alien enjoyed and then demanded more of. Soon after, several other members of the alien's species approached the droids, also seeking the cereal, which greatly alarmed C-3PO.
C-3PO's made an appearance in the children's book Darth Vader and Son from 2013, published by Chronicle Books. Jeffrey Brown both authored and illustrated the book. The cereal is presented as an in-universe counterpart to an actual cereal produced by Kellogg's in 1984, accompanied by a series of live-action commercials.
In 1984, Kellogg's launched C-3PO's, a breakfast cereal described as "crunchy honey-sweetened oat, wheat & corn." This cereal, shaped like "double-O"s, was packaged in a box featuring C-3PO on the front. Several of the box backs included cut-out character masks, featuring C-3PO, Luke Skywalker, Darth Vader, Chewbacca, Yoda, and a stormtrooper. Other boxes contained Rebel Rocket toys, while others included two sticker/trading cards from a ten-card set.
Advertisements for the cereal included various commercials with C-3PO (portrayed by Anthony Daniels) and R2-D2 getting into comedic situations while transporting boxes of the cereal.