If that's near the end of the game then I've nothing to worry about. I'm still testing out my Fallout 4 legs.
It's rather close to the beginning. If you've made it to Diamond City, then chances are you've picked it up at some point.
I'll have to check out a walkthrough to find out where the most amount of resources can be located. I'm having trouble just making beds, lol!
Take Codsworth with you, he's handy in a fight and can carry a good bit of junk. What you want to do is just pick up ALL THE THINGS and then foist them on your robot buddy, haul ass back to Sanctuary (or wherever you made your pile) and then just dump everything into a Workbench for storage. Rinse, lather, repeat. Avoid crafting for the first half dozen runs. Soon, you'll be drowning in stuff to use.
If you get the Local Leader perk, all of your crafting stations from settlements that you control will form one big pot of crafting resources, so stuff you leave in Red Rocket will be usable in Tenpines, etc.
Avoid doing the Militiamen quests, as they will drain your building resources by starting a whole lot of settlement construction quests.
My character doesn't care for starting settlements anyway, and refused to lead the militiamen when offered, basically saying "I'm willing to help, but I'm not in this for your Revolution. I just want my boy back."