Spoiler warning!
This article contains details of Survivalist late-game content.
User Guide from Taukoro from Survivalist General Discussions on Steam.
So once you have gotten to Kate Barlow and need to persuade her to give you the key to find the gold, so here is what you do.

You will need an expendable male survivor because, no matter what the quest ends with 1 person sacrificed. (worth it though) Next you want to get 1-6 Tasteful Erotic Novels, Chick-Lit Novels or Chocolate to gift.

This is due to the fact you want the expendable to get on her good side. Use the friendly speech check ("Come on, let's ride off into the sunset - you and me together with the gold!") get shot and then with another survivor talk to her and demand the key. Fall for her sexy speech and you will find yourself shot. (no surprise there). The reason why a male survivor is needed is because if a female tries to ask Kate to "ride off into the sunset" she will reject them and not reveal the location of the gold bullion.

Now the most importaint part... (Make sure Chris Kane is still alive!) (you will have him tag long with you during the quests leading up to the Los Ceros war if you vote to go to war.) (TIP: voting to go to war will save the lives of 2 people as voting for peace talks will get 1 person shot.)

(I stumbled upon this by accident when i was doing quests and using him as a free guard instead of actually doing his quest.)

So once you find her home, go into the house and then back out. ( just tells you about the potentiial trap) but anyways you don't have to. (just what I did)

Merely walk up to the bunker and he will mention being able to disable the I.E.D's that are rigged all over the place in which he will disable them allowing you to now take the 100,000 gold for yourself.

Now after this you will be given the quest objective to go back to Kate and you have the option of having her join you.

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