Unlimited cash:
You must have a skill of 100% of gambling. After a few mission or two, gamble will be available to you in the BOS. You can purchase whole of the shopkeeper items. Select the items you wanted and then click gamble until you purchases the goods, you need't put money on it. It prove a lot when you are building a squad.

Golden Cheat:
At the character menu name your character HIGHWAYMEN then on optinol character skill choose Doctor, First Aid, and Small Guns At the first level not only will you have a first aid doctors kit and extra stimpacks But you will have a Scout Car Waiting for you at the bridge.
 

Free Bartering:
When you are going to barter with some one you can get it for free. When you get a character to the bartering screen, put in something of his and DON'T put anything of yours in. Click the barter button over, and over again until he gives it to you.
(Note: It's best if have somebody with high bartering skills. Also if the object has a very high worth you'll have to click many many times)