I'll echo the reading material suggestion. Magazines, paperback books, and "other" materials are always well-received. Many towns have a used book store - you can find out what kind of books he likes and stock up for cheap. Even though he'll have the ability to watch the news on TV, the reception is often non-existent, and when the satellites actually do line up, it's AFN News. (Want to find a cheap alternative to waterboarding? Have the guys at Club Gitmo watch AFN 24/7. They'll talk!)
Food isn't really a good idea, as there is no shortage of junk food in other people's mail. It's so bad at times that you can't even give away food! Also, a lot can happen in the weeks to months it'll take the care package to get to him. Chocolate/sugar doesn't handle the 120+ degree flight lines and ship decks that the mail will be sitting on awaiting transportation...plus, if Otto's delivering the mail, you can count on 90% of the mail's contents being shattered upon receipt.
Speaking of shipping, the flat-rate boxes from USPS seem to be pretty standard - and much cheaper than paying by weight, though don't waste your money on the extra tracking features (the packages will be "received" by the FPO or APO, even though they've only started the long journey to your husband). The best thing you can do is make sure to write his address exactly as he gave it to you, and write clearly/legibly in black marker. Mail call is a hectic time, mail that is not easily identifiable might not be sorted as quickly or accurately as the rest.
Finally, like Kathy said, I'll make a pitch for handmade stuff. He'll never get enough of hand-made things from his family: Hand-written letters, crafts, etc. Look at it this way - the hand-written letters you guys write to each other will last decades. E-mail? Unless you print them all out, they won't last quite that long.
Hope some of this helps.