Pepper-jack cheese, or simply pepper-jack, is where a Suethor gives a canon character his/her own tastes. The name comes from a badfic that gave Hermione Granger a taste for pepper-jack cheese, which isn't even common in England.
The logic behind this is described thus by TVTropes' Author Appeal page, which describes a similar concept:
1. I like Fandom A.
2. I also like Fandom B, Song C, Subculture D, Sexual Practice E, Religion F, Political Stance G, and/or Literary/Artistic Style H.
3. Therefore, Fandom A will go together well with any one or more of Items B-H."
The logic is somewhat flawed here, particularly when the author includes concepts which simply do not exist within the fandom in which they are writing. For example, Architeuthis's reports once mentioned an incident in which she found the Rivendell elves making pizza. Perhaps worse was one in which the woodlanders from Redwall developed a taste for, of all things, chicken, which would come under the heading of cannibalism within the canon's rules.