I think an excellent collection to have would be the pre-made championship t-shirts for the losing teams in sports. When I was a kid, I saw a Braves World Series Champs sweatshirt in Big Lots, although the Braves had lost that year. My dad and uncle laughed at it, and I didn't realize that it had been made in advance, so I wondered for a while what kind of caveman made that stupid shirt.

Of some relevance, Where Are the USC Championship T-Shirts?