my suggestion would be... unless you're animating the folding of the box for people to watch it get folded, just start with a poly cube in the dimensions of the folded package and texture from there... trying to fold a package to make a box from it is too much work unless, again, you're creating an animation of the process of folding the box.

if you ARE trying to animate it, i would recommend you convert to polygons and make sure you have edges bisecting the object (from one end to another end) wherever there will be a fold, then when you need to fold, switch to vertex mode, highlight the vertices of the part you want to fold, then press insert and move the pivot for those verts along the edge where you will be folding, then rotate your 90 degrees or what-have-you. repeat the process til the entire thing is folded... select verts, move pivot of selected verts, rotate, select different verts, etc.