Official: A heather grey Champion double weave sweatshirt procured from the Hammes Notre Dame Crook-, er, Bookstore back in 1989. Also, a navy blue Notre Dame Tae Kwon Do sweatshirt (yes, we were an official club back then), also a Champion double weave. Both are in fantastic shape, and I use them during the coldest winter days.
Unofficial: A plethora of t-shirts from various student entrepreneurs, as they would go room to room, dorm to dorm, selling some truly innovative ones. I still have a few left from those days, although sadly, most of them have long been turned into cleaning rags and disposed of. My oldest remaining one is from 1990, which honored our victory over the convicts that year. A sizzling rocket streaked across the sky, and turned a mighty hurricane into a tropical breeze.