I generally take all the individually wrapped foods (like granola bars) out of the bulky box before shipping, unless the item is really fragile (like chips). That way, I can get more into the box. I just put them into Ziplocks to protect them from moisture or sand or whatever. I figured that I can always throw the empty box into my recycle bin instead of giving the soldiers more trash to figure out how to dispose of over there! The ziplocks can always be reused for another purpose once they receive them.
Often I will buy a bulk pack of things like rice krispy treats, granola bars, or peanutbutter crackers and split them - half for my family and half for the soldiers. That way we both get more variety at less expense.
Packing the box tight so that items do not slide around inside is the best way to keep them from getting crushed or mangled. The more space there is for it to jiggle inside the box, the more likely it is to get damaged in shipping - especially if the box is tossed upsidedown or sideways into the shipping container. Some nice things to stuff in the "holes" are beanie toys, small notepads, travel packages of kleenex, or any other semisoft items that can cushion and serve a useful purpose for the soldier as well. I generally throw a magazine in the bottom of the box and a puzzle book or newspaper cartoons on top before sealing just to add a little cushion, figuring I would rather have those take the shipping damage rather than the "good contents" inside the box.
I have shipped many items overseas from my ebay sales and have never had damaged goods arrive. As long as the box does not rattle when you shake it, it will survive the trip to just about anywhere.
Hope these tips help a bit, Kathryn M