All ideas sounds interessting but need to be tested if it works or not.
I did some brainstorming. I'm unsure about some ideas, but lets put them in for some discussions ^^
Some of my first modifier ideas are:
[Ooey have 1-8 already so i start from 9 =P]
09.) Proximity Device
A silmple quiet but steady sound if someone is near your position.
(only yourself can hear the proximity warning)
~ You dont know how far away, which direction or if he above / blow your position.
10.) Shield recharger :
You can recharge your shield energy if you sacrifices inventory itmes
(5 Shield energy with 15s cooldown [~20shield per minute])
~This would be a reason to get loot even you already found your proper gear.
11.) Ammunition converter:
You are able to convert some inventory items into ammunition for you weapon your hand in that moment
(Any item gives 1x Sniper., 2x SG-Shells, 5x AR/Pistol/Smg ammunition with 15s cooldown)
~ I'm very unsure about this one
12.) Tracking device
This can be helpfull to see blood track or- / and foot steps on the ground.
(foot steps [maybe if someone have haevy gear] and bood tracks can be tracked all the time]
~ No foot steps on stone/water; you dont know if the tracks is new or old unless you witnessed something.