I just learned about this today. The USPS offers a "military kit" of shipping supplies for military families:
While it can’t cut postage costs, the U.S. Postal Service (USPS) does provide help to military families and friends shipping care packages overseas to their deployed service members. Since Priority Mail® supplies are the packaging of choice for families and friends preparing care packages for service members overseas, the post office has created a "Mili-kit" based on the items most frequently requested by the military. This kit is available for free to military families.
Three (3) each of flat rate boxes
Two each of Cube boxes
One roll of Priority Mail tape
15 customs forms with envelopes
The kit may be requested by calling 1-800-610-8734 Choose your language (1 is English, 2 is Spanish).
Choose option 1 (it states it is for Express Mail®, Priority Mail or Global Express Guaranteed® products).
When you reach a live agent, request CAREKIT04, the “Military Kit. Allow 7-10 days for delivery. Note: These are free supplies only. Military families must still affix postage to the package.
I will be ordering mine tomorrow morning.