The sequence of photos begins with pages of handwriting samples the art supply manager shows Oskar. This is significant as being what was most related to his present quest. The hundreds of keys are significant in the sequence for the same reason. The others seem to alternate between a simple extension of Oskar's "Stuff That Happened to Me" collection and things overtly or symbolically related to the World Trade Center explosion.
For example, Stephen Hawking and the museum exhibit of two apes might be considered simply extensions of "Stuff That Happened to Me," especially since Oskar wrote to Hawkings asking to be his protege,
Dear Stephen Hawking,
Can i please be your protege?
Further, he worries about Larry in front of the Natural History Museum who "always says 'I promise it's for food' right after asking for money." In contrast, the diagram of how to make a paper airplane might be seen as an overt connection to the World Trade Center (WTC) event, while Laurence Olivier as Hamlet might be seen as a symbolic connection since Hamlet might be said to have been on a quest in reaction to his father's death.
The sequence of the keys, the WTC jumper, and the jumper's close-up, fall as they do since, symbolically, these are the things that compel and drive Oskar, so they are never out of the picture--never separated from his other thoughts--for very long: they always integrate with the others as the paramount reality in "Stuff That Happened to Me":
"There's something incredibly wonderful that I want to preserve."