I have found that saving various empty boxes makes for utility later on down the road. The best ones in my opinion are plastic bullet boxes, as I have found use for them for holding small reloading parts like comparators or gauges:
One for my bullet puller inserts; another for bump gauges that are used to set up dies; one for the FAT Wrench attachments, and one for my comparator inserts for measuring bullet seating depth. The green boxes used to hold .224 caliber Sierra Match King bullets, and the red cardboard box is from Hornady. As you gain further addiction to reloading, you will acquire all sorts of tools and measuring devices that need an orderly place to stay. These boxes fit the bill perfectly, cost nothing, and will last a lifetime.
I also recommend saving cartridge boxes. Sometimes I will load up some obscure loading and don't have any MTM plastic boxes lying around, so I'll stick them in a Remington Core-Lokt box and place a mailing label over the ends and remark them with a Sharpie. Also, the used cardboard boxes are easier to carry in the field and don't make noise like the hard plastic boxes. There has never been a time when I've complained about having too many, and all of the 308 boxes in this picture have been recently re-filled and then emptied on the range:
All of the .45 ACP and .380 boxes are filled, and there aren't many 9mm boxes left in there. I really do use them all the time, and keep every factory ammo box that I empty.