In my college experience, this takes the form of Air Force ROTC apparel ... shirts for each semester, special activity, extracurricular club, Field Training unit and flight ...
In the past, I have taken the position that the $10-15 for each one was generally a waste, since I already have plenty of clothes. When I inprocessed to Field Training this summer, I passed up the chance to get a unit shirt, since the memorabilia package was fairly expensive and I didn't think Field Training was a big enough deal to need its own article of clothing in my closet.
Halfway through Field Training, we made a flight T-shirt for our team of 21. I decided to get that one, because I had grown close to the other flight members during the whole process. I actually began to regret not getting the unit shirt.
Why am I making such a big deal about T-shirts? Because to me they have come to signify appreciating the stage of life you are at. It is recognizing that where you are right now is important enough to cost you a little bit of money and take up mental and physical shelf space.
So next time you have an opportunity to buy a commemorative T-shirt, instead of discounting the present, go ahead and take time to congratulate yourself on the present time that you find yourself in. You might end up having a stack of them taking up space in your closet, but it will be a stack of memories that you can wear!