UConn pretty much nailed it, especially the small hand-written note.
This may not be appropriate for someone with whom you are not related (or very close - don't ask don't tell ), but my brother had always asked for new underwear in his packages. I guess you can never have too many while you're in the field? We also included new toothbrushes, toothpaste, deodorant, Gold Bond powder, Skin-So-Soft, and other similiar comfort-type items we knew he liked.
I also saved old Shout! Magazines and old Sports sections of The Bflo News to put in there, he really seemed to like reading those.
What you're doing is nice. More of us should do it.