Nathan Drake's Journal appears in Uncharted. While it generally doesn't hold a lot of information, it does contain a few straightforward hints that help the player solve some of the puzzles in the game and a few easter eggs.
It contains a page on Nate's girlfriends and their addresses etc. Elena Fisher, who he broke up with recently at the start of U2 and his future wife, is the only one with a photograph amd her flower is still fresh, suggesting he put it in recently. Other than that, there are a few occasional doodles and photos of people he knows, such as two pages containing his drawings of "The Many Faces of Victor "Goddamn" Sullivan" and other goofy drawings like ¡SKELZOR!, a skeleton Nathan used to startle Sully and Chloe in Borneo.
As you progress through the game, more pages are added in with information from previous chapters that will help with later puzzles throughout the game. Various references are also made to the first Uncharted, such as the "slippery naked guy" ranking below a "Demon Sasquatch" on the "scare-o-meter" (both of which outrank Sully's Mustache); or a sketch of an enraged statue which Drake has named "Angry Eddy", with the caption "I KILL YOU DRAKE!" (this is another goofy drawing of Nate's based on Eddy Raja from the first Uncharted.) The last page of Francis Drake's diary that Nathan Drake found in the German U-boat at the end of the first Uncharted is found taped to the first page of his journal in Uncharted 2. Also the Spanish coin that Drake found in the German U-boat at the beginning of the first game is found taped to the second page of his journal. There is also a drawing or picture of Tenzin's daughter Pema.