In Delta Green, bonds are meant to be your character's emotional support network, NPCs you can rely on (at least to a point) to help you deal with the massive psychological trauma inherent in the job.
These bonds could be with your spouse, childhood best friend, Very Good Dog, whatever. The point is that they don't directly represent an in-game resource as written, though they do help agents recover some of their sanity between sessions.
That doesn't model an insurgency campaign very well. For one thing, your closest bonds as a dedicated freedom fighter, after a little while fighting alongside your comrades, are probably going to be with them, not anyone you left behind. For another thing, if you have every reason to assume you're being watched by people who want you dead, you don't go visit your family between missions.
This frees bonds up to do something more appropriate to the context.
Basically what I want is: someone at the table says "hey we need fake IDs to try and get on base and none of us have the forgery skill" and then someone else says "fine then I have a cousin Smirnoff who makes those for a living" and they write it on their character sheet and then the player cell has a new resource and the occupiers may or may not find a new way to get close to the PCs.
>Call it "contacts" instead of "bonds".
>Each contact has 85% in one professional specialty.
>You don't have to decide who your contacts are or what they do until it comes up in-game.
>Your contact score = CHA x 4.
>>Roll under with d% to call in a favor.
>>If the roll fails, they still have a 50% chance of deciding to help you ("but I swear this is the last time do you hear me!?"). Either way, their contact score goes down by 1d20 points.
>>If your contact score ever reaches 0%, they refuse to help or even see you ever again.
>>You can potentially increase your contact score by doing favors for your contact.
>There are conditions that add bonuses or penalties to these rolls (maximum total of 99%, minimum of 1%).
>>Absolutely no chance of being found out: +20% bonus.
>>Favor will likely earn money or status for the contact: +20% bonus.
>>Satisfies a preexisting grudge: +40% bonus.
>>Secrecy* score is 60% or less: -20% penalty.
>>Secrecy* score is 40% or less: -40% penalty.
>>Public Support* score is -10% or less: -20% penalty.
>>Direct physical danger to self or family: -40% penalty.
You could, if you wanted to, game this system to give you a contact you could use to reduce your PC's mental strain, just like a bond in the rules-as-written. You'd just need to use a contact slot on a mental health professional who could then use their skill to help keep you from losing your shit.
*These are two of the scales I've been using to track how the PCs' actions affect the overall campaign.