When I get a good deal on ammo, like the dozen-odd boxes of S&B 115gr FMJ 9mm picked up at Cabela's Door Buster weekend sale yesterday here in TX, I empty all the round into their own plastic dry box I've had for years. I used to buy .223 and .308 bulk from Cabela's in PA years ago for the cheap price and the free dry boxes, before ammo went through the roof.
I mark the boxes with blue painters tape and write the make, type of bullet, load of the round and the date I bought it. Helps me remember how fast I go through it.
I have one box dedicated to random stuff; leftover ammo from friends in odd calibers, a big tupperware style container of mixed .22LR, MTM cases of 25 rounds of 12 gauge each, etc.
Metal or plastic, it's the seal that matters!