Can anybody tell me how to let civilians use backpacks (or just one)? I've been searching on the internet and I could not find anything on how to let a unit use a backpack. I tried to look in the Characters config in the arma 2 addons file to maybe find somthing like canUseBackpack, but I didn't see anything.

As far as I know the Taki civilians can't use backpacks. You can check that out yourself by manually adding a backpack to them with

this addBackpack "US_Patrol_Pack_EP1"

in their initialization line. It's not so much a config problem but the models simply lack the "backpack" proxy.

Does not work. Even tried

car addBackpackCargo ["us_patrol_pack_ep1", 2]

it adds the backpack to the cars cargo, but you cannot take it. What I am looking for is some way of setting a config in my missions description. Also I am using Haris press, and a functionary from the chernarus side.
Added 23 minutes later:

Here is a demo of what is wrong. When you activate the trigger for the civilian nothing happens, but when you activate the trigger for the military unit, he gets a backpack.

W0lle already supplied the reason for this: without the appropriate proxy on the model a character unit cannot carry backpacks (they can still use them in the sense of getting content from them). To work around this one could improvise by using an attachTo, but then this still does not function as it would with a properly set up character model.

Provide more detail on what you are trying to achieve if you want more specific advice. For example specify what different functions you mean with the generic term use (pick up? carry? drop? take items from? any combination of the preceding?). ANother essential bit of information is whether it is intender for use by a playable unit or an AI controlled one.

Regards,

Sander