Just follow good value to weight ratio.
I would never pick up a bottle of beer. It weighs one pound, I will make one cap when I sell it.
I would never pick up a fission battery, unless I need it for one very specific purpose....
It weighs ten pounds, for about 20 - 30 caps, depending on your barter skill.
I will pick up vodka. It weighs one pound and sells for 20 caps. Plus good in a pinch if you need that extra strength. One of my characters is addicted to alcohol, and when she runs out of vodka (the only alcohol she drinks) she gets very cranky. Otherwise she would sell it.
Sell the ammo of weapons you don't use. Early in the game, one mini nuke can sell for 500 caps.... and it is weightless. Don't worry, you can buy more mini nukes later when you are rolling in the caps.
Repair everything, then sell the extras.
Collect scrap metal for Walter. Though I save these materials for something else....
Collect pre-war books for Scribe Yearling. Follow on Moira's quests to find the library.
Collect locations for Reilly. Unbelievable amounts of cash, though the personal risk of loss of life and/or limb, is very high.
Just hang on for a couple more levels, you should be making caps hand over fist. You find more when you check everything when scavenging. The above suggestions, except for Reilly, are for a beginning several levels character. Reilly's quest, to be able to work for her, is heavy combat
, and I might wait, until I have good armor and gear, to dive into that awesome yet punishing quest.
There are so many more ways of making caps.... those are just off the top of my head.