The USPS has a program for military family members and friends to supply them with packaging materials to send packages to troops overseas, Sailors on ships, etc.
Call 1-800-610-8734 and select option #1, then #1 again. Ask them for the "Military pack." They will send you 6 to 8 boxes, tape, packaging materials and labels. They will also give you an I.D. number so if your supply runs low, you just call them up and they'll send you more supplies.
The materials take about four to ten days to receive. Since most places charge you for the box, tape, filler, labels and everything else - this should help save some money.
For more information on mailing items to Service Members, visit the USPS FAQ page.