Even if you've just begun reading Extremely Loud and Incredibly Close, I don't think I'm spoiling anything when I say that Oskar and his father enjoyed playing a game on Sundays together called Reconnaissance Expedition, sort of an advanced knowledge quest designed by Oskar's father with clues that would take Oskar to visit different people and places.
In the spirit of the novel, several participating locations have developed their own Reconnaissance Expeditions for Gulf Coast Reads. Clear Lake City-County Freeman Branch Library has designed a photo quest of local history. Several branches of the Brazoria County Library are featuring scavenger hunts, including one for kids. The Katy Branch Library has hidden clues based on the book throughout the library for a month long game.
Their first clue:
Oskar carries several things with him on his reconnaissance expeditions. One thing in particular gives him security and confidence. What is the object?