Here, I'll save everybody some time and find this the simple way. I lifted this from BIS's commented configs (off the Breath site). These are the contents of the ammo crates and heavy ammo crates. To find the contents of the addons ammo crate, you'd have to depbo "abox.pbo" and look at its cpp. If somebody felt like doing that, adding it to these and maybe formatting this nicely, I suppose it may be worth submitting to the ed depot.
All ammo crates:
Max Weapons: 500
Max Magazines: 2000
Ammo Crates (camo):
Magazine Cargo:
(Type, Count)
WEST
M16, 30
M60, 5
HandGrenade, 10
M21, 10
LAWLauncher, 3
GrenadeLauncher, 3
EAST
AK74, 30
PK, 5
HandGrenade, 10
SVDDragunov, 10
RPGLauncher, 3
GrenadeLauncher, 3
RESISTANCE
AK47, 30
HandGrenade, 10
PK, 5
LAWLauncher, 3
GrenadeLauncher, 3
Ammo Crates (grey box):
Magazine Cargo:
(Type, Count)
WEST
M16, 20
HandGrenade, 10
GrenadeLauncher, 10
LAWLauncher, 8
AALauncher, 3
Mortar, 6
PipeBomb, 6
Mine, 6
CarlGustavLauncher, 3
EAST
AK74, 20
HandGrenade, 10
GrenadeLauncher, 10
RPGLauncher, 8
9K32Launcher, 3
PipeBomb, 6
Mine, 6
AT4Launcher, 3
RESISTANCE
AK47, 20
HandGrenade, 10
GrenadeLauncher, 10
RPGLauncher, 8
9K32Launcher, 3
PipeBomb, 6
Mine, 6
AT4Launcher, 3
One last note, there is a neat little ammo box that you can make by editing the mission.sqm. Its called "MachineGunBox", and it can hold 1 weapon and 2 magazines. It normally contains an m60 and 2 mags, and it looks like the little box sitting in the corner of the "small shed".