You always want to start looking for gift ideas by looking at a person's place in life, goals, interests, etc.
For the college grad, could they use something for their nice job? Wardrobe update (pretty much no one graduates college with a proper professional wardrobe), nice/quality bag, headset, new headphones for public transit commute, etc. Just because they don't desperately need it right this second doesn't mean it wouldn't be nice, appreciated, and maybe eventually needed anyway. Same goes for apartment; maybe they "have everything" but that includes mismatched plastic dishes and a $5 mixer because it was cheapest. Maybe as an adult they'd be interested in upgrading these things gradually, and you can expedite the process if you contribute.
For the HS grad, I feel like we'd need more information to give good suggestions. Do they have a job lined up? Another kind of training? What are their long-term plans if not college? What are their hobbies (many hobbies have consumable supplies that are always in demand)? Of course money would help with any of the above, but I find there's a kind of social ritual and communication in giving actual gifts and I rather like that. Even if it's a gift card rather than money, as long as there's thought/reason behind the card.