Vocaloids have no favorite anything, so if they do it is usually fanon based, and depending on how active the fandom is, an object will gain popularity. The only Vocaloid that was presented to have a favorite food was Yayin Gongyu (now known as Luo Tianyi) who was said to like Haw Apple. However, Yayin was a contest entry at the time, and upon becoming official her biography became voided. Most of the vocaloid 'favourite foods' come from the item wars trend and are unofficial.
If you are referring to character items which are known to be popularized as food stuffs, please see page What are the suggested Vocaloid character items by the fandom?