Navy life can be full of rules and regulations, depending on where your sailor is stationed, so it's important to investigate the basics about her deployment or station when selecting a gift. Ask about her day-to-day life or check her command website for suggestions. The right gift can make your sailor's day in an otherwise unpleasant or boring duty.
Basic Training
For sailors in basic training, there is one best gift. Letters from home are always appreciated more than anything. Most recruits are not allowed gifts of any kind throughout basic training, as their needs are deemed to be met by the Navy command. Letters are allowed on a daily basis and are often the most prized possession of a new recruit's belongings. Write often, even if it's a short letter every other day, and it will help your recruit get through basic with a little less loneliness.
On Ships
Sailors on ships have a very small amount of personal space allotted, sometimes no more than the size of a shoebox. Send him gifts that are either very small or disposable. DVD players and a DVD sets are good, but take the DVDs out of the box and put them into a small, soft-sided CD case for compactness. Homemade goodies that travel well are always most welcome, but send a large batch as they will invariably be shared around with bunkmates. Always enclose phone cards, as they are the only way for most sailors to call home from a ship. Email him regularly, as most ships have active computer workstations for personnel.
U.S. Naval Base
If your sailor is stationed at one of the Navy bases stateside and is living in base housing, you have a bit more leeway in types of gifts to send. Find out what fast food places are on her base and send gift cards from those restaurants. A break from galley food is always nice. Send NEX gift cards as well, since all sailors shop at the Navy Exchange eventually. Make a quilt or afghan for her rack, to give her a feeling of home. Send an iPod, preloaded with her favorite music. A netbook is a very useful gift and she can use it to email you or video conference with you if you enclose a webcam.