Here's a tip/cheat that I accidently (actually Dog Meat) ran across. Essentially it will give you an unlimited amount of select supplies.
In the settlement of Jamaica Plain there is a quest called "search for the treasure" or something like that. When in a room that has a long hallway it will have laser sensors and minor defense modules that pack a punch. Take out the defense modules, then go to the other end of the hallway and hit the button on the wall. By doing this it will start the laser sensors again. Disable them then repeat the button pressing again and it will start the lasers again. If you have a companion with you leave them in another room and make them stay there. I went through three times and got a lot of steel and I believe fiber optics. It's the standard reward for disabling a laser sensor but it keeps giving.