I'm never really broke, but my primary source of income is by picking up "junk" found in containers. Examples would be Cigarette Packs, Cartons, Alcohol, and Pre War Money.
This was actually my first character to ever be poor. I have the cowboy perk and picked up the lever-action shotgun on a lark (fully repaired at Gun Runners) along with some weapon mods for guns I haven't aquired yet (.44 mag). Before I knew it I did not even have enough money to get onto the strip.
I agree that smokes and booze are a great way to make money, and why not? In this world smokes and booze are very in-demand as they should be.