I threw out all of the boxes from my model-building youth, when I hit 18 and went off to college. I wish I had kept them, though.
Some box lids I cut apart, with a vague idea of framing them some day, boxes like those from Revell's warship kits. But those all went into the trash, too.
I think that I saved many, if not all of the instruction sheets, and all of the copies of Shep Paine's "Tips on Building Dioramas" that came with my kits, but I can't find them now, so they may be lost. All of my copies of the newsletter from Revell's Master Modeler Club are gone, too, I think.
This time around, I'm saving the boxes, putting instruction sheets in a binder, and putting spare parts and decals in ziploc bags, so I can keep them in some kind of organization. Sprues are cut into their longest lengths, and go in a box, with all of the small pieces in another.
Not really as organized as it sounds, it still means I'm a pack rat. Maybe I turn up on that "Hoarders" show someday...