'this' in the init field always represents the unit you are editing.
If your unit has a name, you can change 'this' to the unit's name, but there is no meaning of it. Using 'this' is much more simpler and faster...
For Crates you should use this:
this addweaponcargo ["M21",1]; this addmagazinecargo ["M21",10]; this addweaponcargo ["LAwLauncher",1]; this addmagazinecargo ["LAWLauncher",6]