Junk items are items that you can use for crafting in Fallout 4, you can find them everywhere and you can use them for your base building or upgrading of your weapons/armor.
But what is more important you can make a lot of money with it!

In this guide I'll try to explain how to get a lot of money from scrap in a short amount of time.

So there is a lot of scrap to choose from and a lot of it is not worth your time. But there are certain items that can make you a rich man.

Cigarettes:
They are found everywhere, this is a 1950's esque time period and people smoked a lot in the 50's, so check out the white things on any object and hope it's not chalk.
However it only goes for 1 cap each, but then again it only weighs 0.1 and if you can get 25 sigarettes in one raid then it's still 25 really easy caps.

Cigarette packs
There are sigarette pack vending machines all around and you also find them everywhere, you can't smoke in the game and you probably won't be able to use it for much for crafting (as far as I know), so hoard them up and sell them when you can, I believe you can get about 5 caps for one pack so if you get a good raid going you can make a lot of caps.

Cigarette carton
Yes the same again, but this is worth much more, get one of these and you can sell them for 50 caps each, imagine finding 5 in one raid, that's a nice 250 caps right there!

Pre-War money
As far as I know only caps is the currency in this game, so Pre-War money looks like it's worthless and you can only get cloth from it, but it's 8 caps each and the Pre-War money is everywhere!
After one raid I got around 2500 caps just from Pre-War money, not a bad trade indeed!

Gold
I will hear you say: "gold is used for crafting". yes it is! but it's also around 225 caps each! so if you are looking for caps in your couch take one of your gold bars and sell them.

Let me know if there are any other junk that is worth selling.

The scavenging station is a great way to get some extra junk from the wasteland. Assign a settler to get some additional junk and get surprised with valuable stuff you didn't even known you had!

The smart way to do it in my opinion is to have several scavenging stations across the many settlements you have so you can maximise your junk gathering, you'll need loads!

Your workbench will be filled with your junk so you can build your base or upgrade your weapons, basicly it's a magic chest that doesn't have a limit.
Because by now you are using a scavenging station, make sure you check out your workbench inventory from time to time to see if any valuebles are deposited in there.
Also the profits from the stores you can setup are in there same with the food your settlers are gathering.
So check it out reguarly or even daily (ingame time) so you don't miss out!

I'd like to hear from you guys if you have any other tips or theories we can add to this guide so it can be a complete guide. Just leave a comment and I'll add it (after doing the research ofcourse, I mean this is steam, not wikipedia :P )