If you load battle packs, modern bandoliers have 4 compartments that will store 30rds to each compartment on 10rd stripper clips for a total of 120rds per bandolier and I think you can store up to 5 bandoliers (600rds) in a .50cal steel military ammo can or 800rds in individual cardboard cartons, maybe more if loose ammo but I don't store anything loose in a container except .22lr
The assembled bandolier battle packs are a great idea, at the very least having a few hundred rounds on stripper clips to store in a fanny pack or dump pouch is also good, but not everybody is of the mindset to have a grab bag. Magazines are obviously the best way to store ammunition for the ready but as far as transporting them they add alot of bulk compared to clips.