Link for the addon?
Also, it appears to require JAM as well. Is that correct?
In what way does "fix bayonets" get in the way?
I can't test it since you haven't given us the addon information, but here are my thoughts based on a quick glance at the scripts.
The script does not appear to check that you have slots available for the things you are about to take.
For the LAW, it gives you the launcher and just one missile. What happens if you want more than one missile? What happens if you already have a launcher? Add the magazine to the player first, then the launcher, so that the launcher is loaded.
For the SA80 it does not give you a weapon. This is different from the arrangement with the LAW and will cause confusion in the heat of battle. Make the Action text clearer so that you know what the script is going to try to give you. It also doesn't check to see if you have an SA80 in the first place.
Consider using a hint rather than a titletext to say what you've taken. Titletexts are slow to come up, difficult to read if the background is wrong and obscure the view. Also, what is happening is the mission designer talking to the player: that is what hints are for. Titletexts are more for things that are happening in the mission, such as dialogue in cutscenes.
The script offers the chance to take items even if there are none left. It should check first and either not offer the Action, or offer a different Action saying none left. Or perhaps have a hint saying what is not available.
Call it a handgrenade, not a grenade, since that is what it is. Will cause confusion if [rifle] grenades are added later.
Consider adding a first aid kit and/or the GPS to the bergen. Also a packet of Rolos...... titletext "mmm, that's better"; player setDammage (getDammage player - 0.1). (titletext not hint, because it's the player talking to himself.)
Consider using it not for laws and regular mags, but things like mines and satchels - the kind of thing you actually carry in your bergen. SA80 mags are usually much easier to reach than that.