I admit it, I save nearly everything related to races. I can't help myself. This would include t-shirts, BIB's, race medals (if I'm lucky) and assorted other swag items.
T-shirts - I probably have enough t-shirts to clothe a small town and most reside quietly in one of many totes stored around my house. A small, sometimes rotating collection remains within reach for those special occasions. Cotton t-shirts have lost most of their appeal so if last minute entry means no t-shirt then I'll sign up at the last minute. The only real exception would be races that offer tech shirts. I LOVE tech shirts...
Race Medals - Every medal ever earned ends up on my lamp. It's probably a good thing I don't win much. As it is I may have to move onto a second lamp soon. My lampshade has so many medals hanging from it it barely serves its real purpose of providing light.
BIB's - I have every BIB from every race I've ever completed. Two things happen with every BIB I earn: 1) I write the date, time and avg pace on the back of each BIB and 2) I pin it on my cubicle wall(s) at work. I do have some rules. I start fresh each year. So anytime you come into my office you'll only see the races I've done so far this year. It does provide a conversation topic and at least the topic is something I like to talk about :-)
Misc Swag - Anybody need some Rasberry Gu? Chapstick? Bio-Gel? Yeah, me neither but I still keep a box full of the stuff....just in case.