College discounts, forever
I will admit, I am guilty of having committed this act. Long after I graduated, and because I look quite young, I used my college ID to get cheaper prices for most everything. If you pay tens of thousands of dollars for college, you can at least reap the benefits of the institution for a bit longer after you graduate.
I must warn you, this trick only works when no date appears on the ID. For example, if the years are marked on the ID, you’re kind of out of luck, because they might check the date. My college did not want to issue new IDs every year.