All good suggestions.
I’ll add:
Money. Gift cards to local restaurants are good but may get misplaced. Having grandma’s $$$ in their account for another night of takeout is good too.
Sporting goods. If they’re involved in a sport for pleasure they may hook up with others during AC year and partake (skiing, paintball, golf, etc…have to leave it at sponsor’s house but they’ll figure it out.)
Some traditional things not to get or let others get:
Laptop (they’ll get what they need for AC – though some leave them at sponsor’s house for weekend use.)
Good watch (an inexpensive one for AC is fine – save the Heuer for commissioning.)
Clothes of any sort (they can’t even store them.)
Car (not in this household but maybe in some – would be used only 6/7 weeks in the year)
Motorcycle (I seem to recall that they can’t even ride on leave.)
European rail pass (I guess that would be OK if they can squeeze it in between graduation and 30 June.)
Mostly what they need is hugs and encouragement – those are free.