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(Just a note that there are Female Service-members overseas too.) grab a handful of $1 toothbrushes, travel medicine such as Tylenol packs, generic brand things, etc. Generic baby wipes are important, as they use them for cleaning themselves and their weapons. Car, sport, and gaming magazines are excellent. Travel games, pens, paper, notebooks, envelopes, and extra calling cards are great for communication. They don't need stamps because they can mail letters back to the states for free. AA Batteries are a top priority item, as they use it for CD players, other portable items, flashlights, and anything else that requires batteries.
Figure out what your Service-member wants - even if they don't use it or prefers not to - they tend to give it to another Service-member who does; so don't worry what you put inside. Look for the cheapest needs: Think of things that a marine would enjoy while in cots or their sleeping area.