My youngest daughter is seeing a young man she dated in high school who became a Marine and was over in Iraq until just recently. For some reason his parents weren't real supportive of his endeavor, and didn't do much for him while he was in country. When I found out he was there, we started sending him care packages regularly. I've tried to do that for as many as I find on a personal level. I surely appreciated getting stuff from my family while I was over there, and I know this young Marine that is sweet on my daughter did as well. Now that he's back, they are dating and at one point she thought he might even propose to her, but before he could she told him not to because she was too young and not ready for such a committment. He accepted that well enough, but they are no doubt enamoured with each other, and I have no problem with that.
We had a seargent on the forum here for a while that was doing EOD in country a couple years ago. I sent him a few care packages and he appreciated that. Unfortunately he sort of disappeared and I haven't seen or heard from him since. I hope it was just cuz he moved on.
What seems to be the best supplies for care packages are things like beef jerky, pepperoni sticks, pickled vegetables (spicy stuff was always a big hit), canned tuna and chicken, candy that won't melt (runts, m&ms, reeses pieces, jelly beans), fancy mixed nuts, freeze dried meals like what Mountain House sells (a much appreciated alternative to MREs) etc. You can ship jars over, just wrap them in bubble wrap and only send jars that have lids like Mason jar lids. The standard type won't stay sealed. We ship everything USPS flat rate because for soldiers you are shipping to an FPO address so it is treated as domestic, and a flat rate box is around $10 and can hold up to 14 lbs of goodies, which is a pretty good deal. It takes a couple weeks for delivery, but that won't matter too much.
If you don't know of anyone that you can send stuff to, I suggest contacting the USO and/or local recruiters, who will be more than happy to give you blind FPO addresses for you to send general delivery parcels to. That way a unit can share whatever you send to them.
Don't try and send booze or OTC pharmaceuticals, and certainly nothing illegal. Nothing of significant value or it will disappear before it gets there. In the whole 9 months I was in Baghdad, I think I missed two packages out of maybe 30 that my wife sent.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)