A 'cereal graphic novel' could be a graphic novel that has some sort of connection to cereal. Maybe it features cereal characters, like the ones often found on cereal boxes, in its story. For example, it could be about the adventures of a mascot from a popular cereal brand.
Cereal soup definitely isn't a comic. Comics are visual stories with panels and characters, while cereal soup is something you eat. They are completely different things.
I'm not sure specifically which 'lemon cereal fanfiction' is good. You could try searching on popular fanfiction platforms like Archive of Our Own. There might be some unique and interesting stories there.
I'm not sure if there are many widely known 'cereal graphic novels' out there. However, some small - scale or indie works might exist. Maybe a local artist has created one based on a local cereal brand in their area.
Cereal is presented in a rather ordinary way in 'Pulp Fiction'. It's likely just shown as a regular food item that the characters might consume during their daily routines.
The cereal in 'Pulp Fiction' could potentially be a symbol of the ordinary in the midst of the extraordinary. The movie is filled with all sorts of wild and crazy events, but seeing a bowl of cereal is a reminder that these characters also have normal, routine aspects to their lives. It also might be used to add a bit of realism to the scenes, as people do eat cereal in real life.
I'm not sure of a specific one off the top of my head. But you can try searching on fanfic websites like Archive of Our Own. They usually have a wide range of RWBY - related fanfics, and you might find some interesting 'rwby milk and cereal fanfic' there.