My pride and joy is my fastpass collection (woot). At least one fastpass from every WDW attraction that has ever had them, from Test Track to Stitch's Great Escape (I haven't been there since Soarin' or LMAX opened). My favorites include:
Over 40 Test Track FP's
Misprint FP's from Test Track and Space Mountain
Different colored FP's from Dinosaur (one is orange, one is green)
Disneyland FP's for California Screamin' and Grizzly River Run (my only DL FP's)
Bonus FP for HISTA from Test Track (normal Test Track FP with an attached bonus FP to get into HISTA any time before the TT FP becomes valid)
Certificate for 4 people for Splash Mountain or Big Thunder Mountain Railroad (won from Tom Sawyer's Scavenger Hunt on the Island when it first opens in the morning)
2 anytime use FP's for Big Thunder Mountain Railroad
Stitch's Great Escape FP from opening day
And best of all:
4 FP's for Big Thunder Mountain Railroad on my 17th birthday (one says 9:01 a.m., the rest say 9:02)
WOOTY McWOOT-WOOT!
Other things I've kept along the years include every waterpark drink stirrer I've had (Blizzard Beach skis and Typhoon Lagoon surf boards), several chains of beads from Pleasure Island's Mardi Gras celebration, and as much free stuff I could find about Stitch's Great Escape opening (even one of the first parkmaps to show the new attraction).