If the high school graduate is going to be living in a dorm you could give him something for dorm life. My aunt gave me a couple of sets of towels. I used those for years as I remembered her and her family.
You could give him a gift certificate to a store so that he can choose what he wants for his dorm or wherever he will be living.
Same for college graduates. Are they setting up an apartment?
Another thing I've seen done is to hand out cards/paper to everyone who knows them and wants to participate. Ask each person to write down something about the graduate. Perhaps a story that they remember the graduate doing. Funny/embarrassing ones are great. But they can be serious too. Perhaps say why they love/like him or her. Make a prediction about where the graduate will be in 5 years.
When you get the cards/paper back make a scrap book of them. Include any pictures you have.
You could make a time line of their life. Interview them to learn about events important to them. Include pictures.
whoops! probably too late for those.
Give each of them something that they can use for years. I gave one friend a crystal pitcher which could also be used as a vase. It's tougher to know what to give to men. If you know what they enjoy doing or where and what they'll be working at you could ask for ideas from a store that carries related items.