I know this has probably already been done, but I decided to optimize it and post it in tutorials.
Let's get started, let's navigate to core/functions/fn_playerSkins.sqf and find the faction you wish to add invisible backpacks too, in this case, "west" (Police). Then add this code to the case:
It should look like this:
Now you're probably thinking, who would want this as a tutorial, no ones that stupid, but from what I've seen I think it's safe to say people don't know how to do this.