My primary source of caps in prior games was cigarette packs and cartons, pre-war money, liquor, and excess chems. I'd usually hold onto a couple of each type, for when the games decided to be clever and ask for them in dialogue choices, but otherwise it was pretty obvious those were mostly for selling (or I suppose if you played a drunk or addict or something like that). I wonder if any of that stuff will be salvageable for resources? What could you break a cigarette pack down for, plastic wrap, tobacco to plant maybe?
I never really had a problem with caps after a little while. Plenty of things want to kill you and most of them have a few caps and it adds up quick. Then you ran into the quests that paid you handsomely for things like fingers/ears and pre-war books, for instance.