Where to start? Baseball, I have a NY Mets paper placemat signed by Tug McGraw, Yogi, Casey Stengel, and a couple others that I can't make out. Can't vouch for the authenticty as I wasn't there. Later at a game got my signed bat with Swoboda's sig, a cherished possession that my mother disposed of when I went off to live at Rutgers.
Tons of NY Knick photos. All-time favorite was when I went to Knick game with my dad who was a semi-pro photographer. All the Knick players were hanging out in street clothes pre-game watching Olympic game. I still have my 11x14 B&W photo with Willis Reed with his arm around me, my most cherished sports memorabilia possession. Tons of other Knick great photos. Can you imagine being being able to walk up and take pics/talk to the players these days, SIGH.
My old man was a boxing fanatic, and took tons of pics of both the matches, and the celebrities in the stands. I know some are probably worth a small fortune. I'm talking Joe Frazier, Ali, etc. Oscar Bonavena even stayed at my house a couple of times.