Step one, after you have an address, is find a box. You can get Priority boxes from the Post Office and they are free. My box of choice 90% of the time is about 3" x 12" x 13", a "shirt box". Another good size is 12" x 12" x 8". Bigger boxes are always available for more stuff and a unit, rather than just one. Priority boxes are also available online at www.usps.com. You order online, they deliver to your doorstep and THEY ARE FREE!! While you are at the Post Office, get Priority mailing labels and Customs forms. If you get boxes from WalMart, etc. just ask the Post Office for a roll of Priority Mail tape (free). And you will need lots of clear packaging tape. By the time your box makes it to its destinaton, it will have had quite the ride.
THINK BAGGIES BAGGIES BAGGIES!! If you have something too big for the biggest baggie, use the different size garbage bags. Experience has taught that the big containers of lemonade/Tang/pre-sweetended Kood aid/Gatorade can split their seams and spread all over everything in the whole box. Baggies will be used again in the land of sand.
Stuffing the box will help its contents make the trip. When the box is all packed, shake it to make things settle. Full in with something. Personal size toiletries work really well. Think stuff that fits in pockets. Just walk down the aisles at the store.
Customs forms -- depends on which PO you go to. Some are picky, others aren't. If you're taking your package to the PO and filling out the customs form there, take a list of what's in there and the approx. cost of each item. No kidding. I have to do this everytime at one PO and the other one I go to is satified with generalizations such as "Toiletries" and "Snacks."
Stuffing -- good point Kathy!! I use packets of pre-sweetened KoolAid, candy, gum... Also, I use the funnies from the newspaper. I AM careful to screen any newspaper I use as stuffing to make sure there's no non troop crap in there.
And KAthy - the tape thing -- tape over every opening. EVERY ONE! Even the ones that look sealed, tape them too. The sand gets in EVERYTHING!!
Used books are appreciated - I get current novels at a local Used Bookstore for pretty cheap. Sometimes if you mention what you're doing with the books they'll throw some extras in for free. It never hurts to ask!
Don't forget to add a personaly note of thanks and ask your kids to draw a picture....