There are two types of grenade pouches, one for regular thrown ones called the AP grenade pouch (wider) and the launched one which is just called grenade pouch (a bit thinner but about the same width and depth). Small items like a compass, match case, or headlamp/small flashlight (real small though) will fit pretty well in the AP pouch. The only real thing I could find a use for the launcher type is gauze or bandage like what you may find pictures of guys with the old alice harness having a small pouch on the shoulder area.
The mag pouches are basically the same as the large utility pouch minus the protective inner sleeve and are a bit thinner by one mag width (large utility pouch can fit 4 fatter poly AR mags comfortably while the ammo pouch can only fit 3 metal mags comfortably). As far as I know there are 2 types of mag pouch one with molle and one without but both are just as durable and thick as the utility pouches.
Carrier Thread
Christian Moore
Brandon Evans
My "civilian" back pack has a water bottle holder attached to it. Found it on Amazon.