In the Devilbunnies universe, writers used the names of existing concepts, characters, products and companies. Some of them were associated with the Bunnies or their enemies:

For the Bunnies

• Frith, Inlé, the Black Rabbit (rabbit mythology from Watership Down);
• Snapple (a “cute” drink),
• Sailor Moon, Project A-ko (anime);

For the Bunnies’ Opponents

• Elmer Fudd (from Warner Brothers; lent his name to the anti-Bunny forces);
• Moxie, Irn Bru, D&B (“uncute” drinks);
• Vanilla extract (the Bunnies were actually supposed to be allergic or even burned by it);

In some cases the group authors took the name and ran with it.

The Bunnies’ opponents were called Fudds after Elmer Fudd, but then there were the Fuddamentalists, extremely dogmatic Bunny-opponents who would denounce any mention of rabbits as Bunny propaganda. There was a courier named Fudd-Ex. And the Fuddamentalists had a deity named El’Mahr…

When I wrote my story The Rabbit Hole, I was very careful to make it compatible with Devilbunny canon and the existing characters in my old stories, while avoiding using anyone else’s characters. But I also wanted to make sure that I didn’t use the actual product names if this would cause problems upon publication.

So I’m hoping to get a better opinion from Jackie. In the meantime, here are a couple of opinions:

Can I Mention Brand Name Products in my Fiction?
What I’m trying to find out. This essay essentially says the answer is ‘maybe’.

Make Sure Your Fan Fiction Is Legal
Not quite the same; fanfic takes existing worlds and extends them. In a sense that is what the writers were doing with the shared universe of the Devilbunnies.