A copy of War and Peace.
War and Peace is a book, and one of the longest books ever written on Earth. The Book was written by Russian writer Leo Tolstoy. Major John Sheppard brought a copy with him when the Atlantis expedition went to Pegasus. He brought it on the reasoning that they would be there for sometime, so he would take a long book with him. By the time they discovered M5S-224, he was on page seventeen—right on schedule, he claimed. (SGA: "Home")
After two and a half years in the expedition he said he was only through a quarter of the book. (SGA: "The Return, Part 1")