Small icon to show what is in storage

each warehouse and store has Icon to show item inside

a simple but elegant solution: add an "Alternative View" mode, activated via "ALT" and a button on the screen. this view mode shows what is stored where, what is produced where, what is being moved on what transport system or truck, what is mined by what excavator and so on.
could also be multi step: off, low info (like how the game looks now), high info (shows absolutely everything at a glance)

and fullness of storages

One should never use the Alternate Shift button to activate or deactivate something. This makes it difficult to use other keybinds that use the "Alt" key.
And the other game that used the "Alt" key for this was wrong as well.
The 'I' char for Information View, or some other keybind would work fine.
Yes, having an Icon on the buildings would be nice. (Note that this has been suggested elsewhere many times.)