The core box holds only the various general tokens (sippress/activated, order), dice, templates, etc. but not the recruitment tiles, troop tokens, or their equipment.

The German and Russian storage boxes have drawers so you can put a recruitment tile and all its troop and platoon-specific option tokens together to make it easy to grab them if you want to use that platoon. The gear and stuff available to any force of that army go in a drawer or two as well. Very helpful when setting up a game.

You can just use bags and store all the troops and their gear in the core box, of course, but the drawers are very handy and look great on the shelf 🙂