Dearest Carla has written an excellent informational essay on what, how, and where to send your holiday wishes to those who are at the oh-so-pointy end of the spear.
Some Soldier's Mom: HOLIDAY PACKAGES FOR THE TROOPS
Remember, it doesn't take anything more than a stamp and a piece of paper to let someone far away from home know that you care about them and believe in them. That is more important that all the "stuff" you can send.
However, getting "stuff" is always nice too...
p.s. You can always write off postal fees as a charitable donation if you send the care packages though a charity like Soldier'sAngels.