Stuff stashed on the Space Shuttle's Robert Pearlman is quite possibly the world's most elite space craphound. His site is devoted to space history memorabilia, and is full of great posts like this one about mementos and souvenirs stashed on Discovery by astronauts:
Roman has a recording. Sunita's got her snapshots. And Bill has his banner from up north. The STS-116 crew, living aboard Discovery and docked with the International Space Station, has mementos and favorite items packed with them. Launched on the evening of December 9, the six member crew has also delivered supplies for the ISS, a new truss segment, and a new station resident, who will stay on the ISS when Discovery returns to Earth.

For STS-116 commander Mark "Roman" Polansky, pilot Bill Oefelein and their four crewmates, the mementos in their personal preference kits (PPKs) and in the Official Flight Kit (OFK) are souvenirs of their just begun 12-day mission to be given to family, friends, and organizations that they support. For Sunita Williams, who moved onto the ISS on Monday, they'll act as reminders of home for the duration of her six-month stay.

"We all have a small amount that we can take up on shuttle," Williams told collectSPACE. "For the station we have a little extra [room] that we can take up of stuff that we can really use while we are up there, like a ball cap or whatever."

"Its just like your office, where you have pictures of your family or little things that are mementos to you and some of that stuff is a little extra for station crew members [as] we are going to be there for a longer period of time," said Williams.

Link. Image ( Space Camp will turn 25 years old in 2007, and this is one of 250 small commemorative flags up on Discoery right now. After the STS-116 mission returns to earth, the flags will be distributed as gifts for Space Camp participants and alums. (Thanks, John Schwartz!)