If he is "more" then a friend you can do cute, slightly romantic things. Always do some candy, maybe a cute stuffed animal, Do a type of confetti in the box. (Not glitter or anything like that but those shaped ones, ya know?) A pair of silky boxers, a cute valentines card, A soft furry blanket (it gets REALLY cold in Korea, I've been there)
Now, if he's just a friend, someone you can be goofy with I would say candy (of course) a silly/funny valentine, some sort of character cotton boxers, Silly toys to occupy his time, the Harry Potter jelly beans if you can find them. (Those are always 100% hit as a practical joke for military people) a slinky......
I could go on and on. If you want anymore ideas, let me know. I have quite some experience with care packages. LoL