["My son just left for college and I don't want to throw away his old comic books and trophies.", "Aww that's really sweet. I understand being sentimental about that sort of stuff. Do you feel like you have to?", "Yes I am really attached to his stuff. He told me get rid of his old stuff but I think I will let him know I just can't do it."]
You should just keep it for now. He may think that stuff is corny now, but later in life he will be glad you kept it.
I don't want to throw away my son's old trophies.