Pack the Boxes Right
For a super secure box, you should tape the seam on the bottom, and you should run a piece of tape perpendicular to that seam. Pad the bottom of the box with newspaper and stuff the sides with extra paper to really make the bottom solid. Depending on what you're packing, you should wrap each item with paper. When you've filled the box to capacity, tape it shut and label it with its contents and your name. And be sure that you label the sides of the box, not the top of the box.