Whats in a bunker?

[Marcello]

It is unclear what you are asking here.
Bunkers with a suitable carry capcity can be loaded with guns, soldiers and what not exactly like APCs. Once loaded they will be protected against enemy weapons but at the same time they cannot fire as long as they are inside.
The bunkers themselves can be armed with any weapon exactly like if they were vehicles. Such weapons, unlike the ones carried inside, will fire at the enemy. You can rearm existing bunkers with either the OOB editor or editing the scenario directly.