Plastic is a very important material in FO76. It’s used to craft and repair a lot of different items, but also bulk other materials which you can then sell to vendors for caps. There are many locations where you can farm plastic, as well as collect it in the world as you go (use tag for search) – but one of the best locations is Morgantown High School.
Plastic also drops in larger quantities in restaurants and dinners.
If you go into the high school, you will see lots of plastic pumpkins and other items, collect them all, kill the enemies and just re-log (server hop) to do it again.
Few runs later and you’ll have tons of plastic guaranteed!