As part of an emergency supply cache, sure, or if the goal was a single can that could be used to resupply someone/group of someone off-site. The issue I have with using them for off-site resupply would be knowing exactly what was needed vs what's packed in the can. (need 300 rounds of 5.56, there are 210 in the can; need 10 shotgun shells, have 50 in the can, etc) This limits the usefulness of the can, and would require grabbing multiple cans, defeating much of the point of mixed packing. Perhaps if a specific packing list was used "Pack A: 210 5.56 in mags, 2 boxes of 9mm" and "Pack B: 25 slugs, 25 buckshot, 2 boxes of .45"?

As it stands, the only ammo can I keep with mixed ammo are my "ready mag" boxes" with a basic combat load for several weapons loaded in mags.