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....
I always used lots of tape, but learned the value of stuffing and LOTS OF TAPE when a box to txradioguy, of all people, came back. Someone transposed the zip code. ARGHHHH!!! Boy do the boxes get beat up!
The used book thing is good too. I have a couple friends feeding them to me. I figure they fit great in pockets, and can be passed around until they fall apart. Maybe the guys will have some suggestions too.