A good wristwatch. It's good to have one in situations where taking out a phone isn't really acceptable. Also, having the time right there where you can see it at a glance helps keep time mgmt. on track.
We got DS a ring for his college graduation; which meant much more to him. It's actually a wedding ring, but he wears it on his right hand. He chose it, it's a black tungsten spinner ring, with his graduation date engraved on it -- in Aurebesh. (He is a SW geek and also on the spectrum; the spinner ring is a discreet fidget item.)