From Any Soldier.com, a cute description of how to package soldier care gifts:

Packing

Send in easy to handle boxes (say under 10 pounds) and wrap like Godzilla will handle it because he will. Shake your box, does stuff move around? Not good, it won't survive the trip. Big, heavy boxes are just asking for trouble.

(Emphasis mine.)

Hmmm.  I didn't know our packages were routed through Tokoyo!