used as an example only
i have absolutely no nothing at all in other workbenches absolutely everything (except corn/mutfruit/tatos harvested from settlement areas) is stored at sanctuary, when i take a new settle ment i empty workbench and take to sanctuary
so when i build at taffington and see 1000+ ( i think it was something like 1750ish) cloth it is 100% because of all the pre war money/teddy bears etc etc in my sanctuary workshop
same with oil for example for the defenses, i literaly have 0 oil, none at all but when im building at taffington i have access to 458 or so why? becasue of all the paint cans/bunsen burners/blow torshes etc that i have stashed at sanctuary
edit: also when i build say a heavy machine gun turret before i click "ok" how it comes up with the list of what its going to use.. well it comes up with all the junk items its getting the resources from, i nwhich there are none directly in its own workbench which pretty much proves that you can use any junk item from any of your supply line workbenches for their resource components
edit2: saw the weapons and armour thing. weapons and armour ARE NOT JUNK ITEMS!!! even if you have them stored in the workshop at the settlement you are building in they DO NOT COUNT AS RESOURCES UNLESS YOU BREAK THEM DOWN MANUALLY!!
I am talking about junk resources like steel buckets/fans etc etc
so if you take all the steel out of every single workbench you have and then take out every single junk item s othere is nothing at all in any workbench you own, then you grab a metal bucket and put it in sanctuary workbench and then go to abernathy farm (as long as supply line ofcourse) you will now have 2 steel to build with from that steel bucket in sanctuary
i can guarantee you 100% that although you cannot grab any item at all out of a workbench that you are not at despite supply lines you can absolutely use any JUNK item from any workbench in your supply lines for its resource components when building.