Chloe asks, "What about the sandwich?"
Fuyutsuki continues, "I have lived in the world which Suzuka thinks she wants; it was devoured by the Outsiders because there was nothing to stop them. Because it was a world without meaning or purpose, exactly what the Outsiders need to get their fingers into it." He sighs more. "The sandwich, you see, rejuvenates the Pattern by the balance between its components and is tasty."
Kaname says, "Because of the sandwich?" She looks confused. "Alright. I'll...uh...keep that in mind."
Chloe asks, "You know how Minako has all those fancy equations that she uses to predict nexii and run complex simulations with?"
Kaname nods. "Yes."
Chloe says, "Well, I use a sandwich."
Kaname says, "A sandwich."
Chloe says, "It's all symbolism. Sandwich, quantum equations, it's all just a way to express aspects of the narrative principles of Order. This isn't the universe of the Sidar. The Pattern doesn't work because of math or science."
Kaname nods. "I'm just...so different things are different condiments and stuff?"
Chloe says, "Not really. It's just a sandwich."
Kaname says, "Ahh. Right."
The Sandwich of Order is a high-level analogy for the unifying nature of the Pattern, able to stand into for the totality of the real thing during complex Pattern operations.
Or maybe it's just a bad Pattern Master joke.
It is unclear if the Sandwich actually exists on any real level, or if it is just an abstract piece of symbolic logic. It it does exist, it is probably doomed to be eaten by Random.