Not-Augustine gives Jonathan a box marked IN CASE, filled with memories of Trachimbrod. Inside, they find things like a necklace, an old map, the last vestiges of Cameron Diaz's career, and the fateful photograph that jogs Grandfather's memory of his friend Herschel and sets the end of the novel into motion.
So, why "in case"? The box is marked IN CASE just in case someone comes along who knows what to make of its contents. When Not-Augustine pulls a ring out, she says, "The ring does not exist for you. You exist for the ring. The ring is not in case of you. You are in case of the ring" (23.16). In other words, she's counting on Jonathan to give the objects meaning. If Grandfather weren't around, it would just be another photo. But since he is there, he can pass the story along to Alex, who can then pass it along to others. Without the memory, the photo is basically meaningless. (This was before Instagram filters gave Insta-cred to snapshots of your breakfast bagel.)
Here's the thing: supposedly, Jonathan is crafting the story of his ancestors from the objects in the box, so we're assuming that many of the objects that are significant in the novel—Yankel's abacus bead, Brod's mermaid costume, Safran's constantly busy manhood—were inside the box. But we learn early on that the box was stolen on the train when he returned to America—which means he can't have spent much time with them.
How many of these objects actually existed, and how many are only in the just-in-case box of his mind?