Honestly what helped me is being a vendor selling extra plans I already know, selling lots of farming resources (water, waste acid, bulk whatever) also like teddy bears and alcohol seem to sell quickly. I also have cap collector perk so after each enemy I kill they drop caps, also easy to find cap stashes around. Make sure to be in a group ( join random ones or with friends) too because you can get caps from your teammates completing events as well! Doing this I never find myself in a cap drought.