One of the “!” on the map takes you to Zaid, who is making UV Flares for Rais. He needs your help though as he is out of resources for making them. He needs you to head to the hanger to obtain a supply of zinc powder and turpentine for the flares.
This side-quest is among the more challenging in that it requires a mix of different tactics. Basically the layout is simple: in the Hanger there are boxcars that contain some of the resources you are sent to get. There is also a partial Supply Drop here - that is worth getting as it will make the Quartermaster happy.
In order to access the resources you will need to eliminate a sufficient number of infected so that you can open the boxcar doors without being attacked. Once you accomplish that and obtain the two buckets of Zinc Powder, you then need to basically do the same thing on the other side of the Train Hanger - though on the other side in place of the boxcars you are instead working your way through a series of separate rooms.
The Turpentine is in the very last room in this series of rooms. Also IF you have not yet completed the side-quest Bandages and Meds you can obtain the three boxes of Painkillers that are required for that from the med cabinets in this series of rooms - which is actually a good idea if you need them because Painkillers are among the rarer of the resources to be scrounged.
Once you have obtained the Terpentine and the Zinc Powder, return to Zaid for your reward - which in addition to money/points also includes the Blueprint for Zaid's Flares.
I have done everything in the mission required except talk to zaid. The reason is because there is a certain train container I'm unable to open but my sense on the game clearly says their is something in there. Any ideas on how to obtain this extra loot?