By the way the gun crate is mostly Lasguns of different make, maybe a couple Bolters, Plasmaguns and maybe a Flamer or two + Pistol variants for each ones. Ammo crate has appropriate ammo for said guns.

Mostly if you can dig through it, you'll find the gun you want, as long as it's not ridiculous like a whole plasma cannon or heavy bolter. Same goes for the ammo crate, if you dig through it enough, you'll find shotgun shells lying on the bottom or something.