I have a bunch of old baseball cards that are awesome to me, and a few other key sports memorabilia items that I keep dear (Magic Johnson signed basketball, old Kobe #8 jersey, about 10 old school Raiders jerseys given to me by my dad, etc).
I also have every single sporting event ticket I've attended since I was probably 10 years old, including every home game of the Angels world series run in 2002.
Eventually I will get all the playoff tickets put into some sort of plaque with the picture I took of the team celebration just after they won the world series, a few pics I have of me at the games, and the police citation I got after running on the field after the divisional series playoff wins.
I have a hardback of SlaughterHouse 5 signed by KV and a hard copy of A People's History of the United States signed by Howard Zinn.