I once worked a stint for UPS doing package sorting. I definitely used that time to take some mental notes for any future shipping of mine. One big thing to pay attention to is keeping the weight/center of balance FIXED. Preferably low to the bottom and centered, but definitely fixed fixed fixed. Packing peanuts might still let something heavy shift around. Some folded up cardboard to keep heavy stuff fixed in one spot can go a long way to keep that box together.

The reason comes down to the belts in the sorting facilities. Some conveyor belts will suddenly tilt up at like 35°. If your contents shift the right way at that moment, the contents will start to use your box like a hamster wheel, counteracting the movement of the belt, and it will stay there doing flips until another package takes a beating helping it, or the jam is cleared. Even worse, it could climb that 35° incline and instead wobble wrong all the way at the top, and come tumbling down 30ft. You grow to learn the sound of a tumbling package, because immediately after the tumble it hits a small metal lip 2 ft from your head, shoots across your work area, and lands where you just grabbed it from. I think the max limit on that belt was 60lb packages.

Auto mechanics, this is specifically why your alternators are always beat to shit after UPS ships them.

This was also 10+ years ago, maybe they addressed the careening packages of death