be tight.
1. how heavy it is.
2. how loose it is.
the heavier the lower in the load, the looser the higher in the load. a box that has 1 heavy item in it has to move up in the load because it will ruin the structure of the tier being stacked, thus creating more risk to the more fragile items in the middle because of it's weight. this concept directly applies to dollies as well. if we cant stack it, it may as well stay loose.
the items just mentioned can be in bins as well. try to avoid bins that either have lids that will not stay on, or are too 