In our household it would be pretty easy-
All our stockings have some practical things, some candy, and something completely useless and a little silly.
Practical things: tooth brushes, deodorant, socks, underwear, dental floss, etc
Candy: everyone gets a few things the same and then each kid gets their favorite
Useless things: these are frequently from the dollar store or the cheapie aisle at
walmart or silly holiday stuff... things like glow sticks, bouncy balls, silly putty, small games, cards, etc
I will occaisionally put in "gifts" into the stocking too- like if they want something that is small and I don't want it misplaced in the tear into all the packages frenzy that can happen with a family with 4 kids...
14yo boys are tricky- that is when gift wise they want expensive stuff. You could always put things that could be used on the trip- puzzle books for the trip home, school supplies. Does he play those card games like Yugioh or World of Warcraft? (although those can get expensive- my now 18yo loves getting those

) I would say the most successful if you really don't know much about him would be gift card or cash (a few ones thrown in there or quarters even look more impressive than say one $10 bill) and some candy would probably be appreciated...