I'm guessing you buy your plastic boxes at the same place I do: Dollar Tree.Collect all of it:
And what you see is KEY: SORT IT! By headstamp. If possible keep track of how you cycle it, i.e. number of reloads. When reloading keep a note of the brass headstamp with the load data. Different cases (by maker) have slightly different volumes---yeah, yeah, they are all different if you get really picky but trends appear by brand. And there are differences in other ways too: hardness, primer pocket 'tightness', size of flash hole...
This is what I'm about to reload, so it's mostly sorted. There are several 5 gallon buckets out of frame, waiting to be sorted.
Oh, need to mention this: reloading is highly addictive; but you might already have guessed that.